the influence of weathering on the engineering soil
TRANSCRIPT
The influence of weathering on the engineering soil profile:
a study of low relief basalts in South Africa
by
HAM van Rensburg
2018
© University of Pretoria
The influence of weathering on the engineering soil profile:
a study of low relief basalts in South Africa
by
HAM van Rensburg
Submitted in fulfilment of the requirements for the degree
Magister Scientiae in Engineering and Environmental Geology
in the Faculty of Natural and Agricultural Sciences
University of Pretoria
Pretoria
2018
© University of Pretoria
i
ABSTRACT
The high relief or mountainous basalt in and around the regions of Lesotho has extensive
information on the nature and properties of the basalts, as a result of several developments on
these basalts such as the Lesotho Highlands Water Project. This resulted in a wide variety of
research conducted and published. In contrast, less published research is conducted on the
lower relief or flat lying basalts leading to fewer available information on the nature and
properties of low relief basalt deposits.
Five flat lying basalt sites were investigated in order to gather data on low relief/flat lying
basalts. The two main sites of this investigation were researched in the Kruger National Park
(KNP) on the southern basalts (Nhlowa) a high rainfall area, and on the northern basalts
(Mooiplaas) a low rainfall area. These are two of four research supersites created in the Kruger
National Park in order to create cross-disciplinary data rich sites. A mineralogical and chemical
analysis for comparison of the parent rock and soil profiles between these two sites were
undertaken. The Sibasa Formation basalts at Siloam and the Springbok Flats basalts at Roedtan
and Codrington are three additional low relief basalt sites, in different rainfall areas. These sites
were investigated to compare to each other and to the KNP sites.
XRF and XRD data were used together with profile development in their respective different
climatic environments and basalt origins to determine the weathering progression and
characteristic of low relief basalts. This was done by studying the depletion and enrichment of
major and trace elements (Fe, Ca, Mg, Na, K, Ti, Y, Zr) through the profile from basaltic rock
to residual soil. Furthermore, identifying the breakdown of primary minerals, such as Augite
and Plagioclase, to secondary Smectite minerals further supports the identification of
weathering progression in low relief basaltic rock. This can potentially aid in pre-planning of
engineering geological investigations on residual basaltic soils. Additional information on the
Atterberg Limits will also be presented in order to start to determine the effect low relief basalt
weathering has on the engineering properties of the residual basalt soils.
In setting out to determine the influence different climatic conditions contribute to the
weathering process and soil profile development of low relief basalts, it became clear that
research of a specific rock type in a single setting is not sufficient. In order to truly understand
the behaviour of basalt weathering, a combination of low relief, mountainous other settings in
variable climatic conditions are necessary. This study shows the significant effect a moderate
shift in climatic conditions such as rainfall and evaporation intensity have on the development
of residual soils on low relief basalts, such as pedocrete and secondary mineral formations.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
ii
The influence of weathering on the engineering soil profile:
a study of low relief basalts in South Africa
TABLE OF CONTENTS Page
1. INTRODUCTION ..................................................................................................... 1
2. LITERATURE REVIEW .......................................................................................... 2
2.1 Basaltic rock.......................................................................................................................... 2
2.2 South African Basalts ........................................................................................................... 5
2.3 Weathering of Basalt ........................................................................................................... 10
2.4 Pedogenesis ......................................................................................................................... 18
2.4 Engineering Geology .......................................................................................................... 20
3. CASE STUDY ........................................................................................................ 25
3.1 KNP Supersites ................................................................................................................... 25
3.1.1 Supersite background .................................................................................................... 25
3.1.2 Geology ― Mooiplaas and Nhlowa .............................................................................. 28
3.1.3 Southern Basalt Research Supersite (Nhlowa) ............................................................. 29
3.1.4 Northern Basalt Research Supersite (Mooiplaas) ......................................................... 32
3.2 Siloam site ........................................................................................................................... 35
3.2.1 Site description .............................................................................................................. 35
3.2.2 Rainfall and evaporation ............................................................................................... 35
3.2.3 Geology ......................................................................................................................... 37
3.3 Roedtan and Codrington ..................................................................................................... 38
3.3.1 Site description .............................................................................................................. 38
3.3.2 Rainfall and evaporation ............................................................................................... 40
3.3.3 Geology ......................................................................................................................... 42
4. METHODOLOGY .................................................................................................. 46
4.1 Desk study procedure .......................................................................................................... 46
4.2 Field work procedure .......................................................................................................... 47
4.3 Tests conducted ................................................................................................................... 49
5. RESULTS AND ANALYSIS ................................................................................. 50
5.1 Profiles ........................................................................................................................................ 50
5.1.1 Nhlowa Profiles ― Lebombo Basalt ............................................................................ 51
5.1.2 Mooiplaas Profiles ― Lebombo Basalt Profiles ........................................................... 57
5.1.3 Siloam ― Sibasa Basalt Profiles .................................................................................. 65
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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5.1.4 Roedtan ― Springbok Flats Basalt Profiles.................................................................. 67
5.1.5 Codrington ― Springbok Basalt Profiles ..................................................................... 69
5.2 Chemical and Mineralogical Analysis ........................................................................................ 71
5.2.1 XRF Analysis — Rock ................................................................................................. 73
5.2.2 XRD Analysis — Rock ................................................................................................. 77
5.2.3 XRF Analysis — Soil ................................................................................................... 80
5.2.4 XRD Analysis — Soil ................................................................................................... 85
5.3 Engineering Parameters ...................................................................................................... 88
5.3.1 Atterberg Limits ............................................................................................................ 88
5.3.2 Compaction data ........................................................................................................... 90
6. SUMMARY ............................................................................................................ 92
6.1 Geology and Rock mineralogy ........................................................................................... 93
6.2 Profile development and weathering ................................................................................... 95
6.2.1 Profile differences ......................................................................................................... 95
6.2.2 Element exchange ......................................................................................................... 97
6.2.3 Mineralogical changes .................................................................................................. 99
6.3 Engineering Geology ........................................................................................................ 101
7. Conclusion ............................................................................................................. 102
7.1 Profile development .......................................................................................................... 102
7.2 Element analysis ............................................................................................................... 104
7.3 Mineralogy ........................................................................................................................ 105
7.4 Engineering Data .............................................................................................................. 107
8. Acknowledgements ............................................................................................... 108
9. References ............................................................................................................. 109
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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LIST OF FIGURES
Figure 1: Characteristic summary of Tholeiitic and Alkaline basalts (Winter, 2001).
Figure 2: AFM diagram showing element abundance between Tholeiitic and calc-alkaline basalts
(adapted from Winter, 2001).
Figure 3: Weinert’s climatic N-value, with N=2, N=5 and N=10 contour lines (adapted from Weinert,
1980).
Figure 4: Supersites, Land Types and
Figure 5: Geological map overlay of the Nhlowa research supersite (©Google Earth, 2015 and
Barberton, 1986).
Figure 6: Geological map overlay of the Mooiplaas research supersite (©Google Earth, 2015 and
Tzaneen, 1985).
Figure 7: Lebombo Group distribution and supersite localities (Duncan and Marsh, 2006).
Figure 8: Site boundary and auger hole positions: Nhlowa research supersite on the Southern Basalts
(©Google Earth, 2015).
Figure 9: Stream orders: Nhlowa research supersite on the Southern Basalts (as depicted in Smit et
al., 2013).
Figure 10: Site boundary and auger hole positions: Mooiplaas research supersite on Northern Basalts
(©Google Earth, 2015).
Figure 11: Stream orders: Mooiplaas research supersite on Northern Basalts (as depicted in Smit et
al., 2013).
Figure 12: Site boundary and test pit positions: Siloam site on Sibasa Basalts (©Google Earth, 2015).
Figure 13: Geological map overlay of the Siloam site (©Google Earth, 2015 and Messina, 1981).
Figure 14: Site boundary and test pit positions: Roedtan site on Springbok Flats Basalts (©Google
Earth, 2015).
Figure 15: Codrington site on Springbok Flats Basalts, approximate area of investigated quarry
(©Google Earth, 2015).
Figure 16: Geological map overlay of the Roedtan and Codrington site on the Springbok Flats,
(©Google Earth, 2015, Nylstroom, 1978 and Pretoria, 1980).
Figure 17: Mean annual precipitation across Limpopo Province (SoER, 2004).
Figure 18: Mean Annual evaporation of reasearch sites (WR2005 map overlay to ©Google Earth,
2015).
Figure 19: Laboratory soil textures for individual horizons for SBProfile 1.
Figure 20: Average soil textures for different horizon for SBProfile 1.
Figure 21: Laboratory soil textures for individual horizons for NBProfile 2A.
Figure 22: Average soil textures for different horizons for NBProfile 2A.
Figure 23: Laboratory soil textures for individual horizons for NBProfile 2B.
Figure 24: Average clay and silt content for NBProfile 2A vs NBProfile 2B.
Figure 25: The Karoo basalts plotted on the AMF diagram for Tholeiitic and calc-alkaline basalt
determination (adapted from Winter, 2001).
Figure 26: Major element change between Nhlowa (SB - southern basalts) and Mooiplaas (NB -
northern basalts) sites.
Figure 27: Major element mobilization in Southern Basalt horizons (Nhlowa).
Figure 28: Major element mobilization in Northern Basalt horizons (Mooiplaas).
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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LIST OF TABLES
Table 1: Expected Average values of Residual Basalt for Drakensberg, Sibasa and Letaba
Formations, Brink (1981 and 1983).
Table 2: Total Annual Rainfall data for selected towns in Limpopo.
Table 3: Profile description summary for SBProfile 1 - Nhlowa site.
Table 4:Profile description summary for SBProfile 2 - Nhlowa site.
Table 5: Profile description summary for SBProfile 3 - Nhlowa site.
Table 6: Profile description summary for SBProfile 4 - Nhlowa site.
Table 7: Profile description summary for NBProfile 1 - Mooiplaas site.
Table 8: Profile description summary for NBProfile 2A - Mooiplaas site.
Table 9: Profile description summary for NBProfile 2B - Mooiplaas site.
Table 10: Profile description summary for NBProfile 3 - Mooiplaas site.
Table 11: Profile description summary for Sibasa basalts - Siloam site.
Table 12: Profile description summary for Springbok Flats basalts - Roedtan site.
Table 13: Profile description summary for Springbok Flats basalts - Codrington site.
Table 14: Average rock element concentrations for the Mooiplaas and Nhlowa sites.
Table 15: Average mineral concentrations for the Mooiplaas and Nhlowa sites.
Table 16: Movement of average trace element concentrations of the sites.
Table 17: Mineral summary across horizons for Plagioclase, Diopside, Augite and Smectite.
Table 18: Residual horizon Atterberg Limit averages from all sites.
Table 19: Completely to highly weathered basalt Atterberg Limit averages.
Table 20: Mod. AASHTO and CBR test results for the Sibasa Basalts at Siloam.
Table 21: Mod. AASHTO and CBR test results for the Springbok Flats basalts at Roedtan.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
1
The influence of weathering on the engineering soil profile:
a study of low relief basalts in South Africa
1. INTRODUCTION
Extensive geotechnical data exist for the high relief or mountainous basalts in and
around Lesotho, due to the development of dams and roads of large projects such as the
Lesotho Highlands Water Project. Only sporadic data are available on the low relief or
flat lying basalts scattered across South Africa, such as the Lebombo basalts present in
the Kruger National Park (KNP), the Sibasa basalts at the foot and in the valleys of the
Soutpansberg and the Springbok Flats basalts between Gauteng and Limpopo.
The low relief basalts are believed to experience deeper in-situ weathering and
therefore have thicker residual soils than the mountainous basalt in and around Lesotho.
The data available for these high relief basalts with intersecting valleys are not
representative of the low relief basalts. This research study set out to investigate these
low relief basalt sites in order to add to the sparse data of this subject. The main focus of
this study revolves around two of the four Research Supersites created in the Kruger
National Park, specifically the northern (Mooiplaas) and southern (Nhlowa) basalt sites
falling in different rainfall intensity zones. Three other low relief basalt sites outside the
pristine conditions of the KNP were also studied. These additional sites were at Siloam
underlain by the Sibasa Formation basalts in the Soutpansberg, and the Springbok Flats
basalts, of the Karoo Supergroup, at Roedtan and Codrington. These sites were also
chosen based on different climatic conditions and availability of data.
These five sites were used to investigate the weathering and residual profile
development of basaltic rock, based on the different climate circumstances of variable
rainfall and evaporation. In order to determine and indicate progression of weathering
from rock to residual material, X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD)
analyses were utilized to determine the rock and soil chemistry. This also aided to
indicate the different elemental exchanges that occur between high and low rainfall areas.
Specifically portraying the depletion and enrichment of main elements such as Calcium
and Iron between sites in the profile, which may lead to the formation of either ferricrete
or calcrete. A distinct difference of ferricrete or calcrete formation was noticed between
sites with different climatic environments.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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A look at previously believed immobile elements such as Titanium (Ti) and the
trace elements Yttrium (Y) and Zirconium (Zr) was also done in order to portray
progression of weathering on an elemental scale.
Therefore, the aim of this study is to determine the influence different climatic
environments have on the weathering and soil development of the scarce researched topic
of low relief basalts.
In pursuit of the aim the objectives of the study are as follows:
• Add data and knowledge to the engineering geology of low relief basalts;
• Provide chemical and mineralogical data of low relief basalts in different climatic
environments;
• Indicate the differences in weathering products and chemical changes occurring
during weathering in the various low relief basalts in different climatic
environments;
• Indicate the climatic effect and influence of basalt mineralogy on pedocrete
formation.
2. LITERATURE REVIEW
2.1 Basaltic rock
Basaltic rock is the most abundant volcanic rock on Earth, creating the upper
layer of the oceanic basins, forming large lava flows in many regions on the continental
crust as well as forming islands from many well-known volcanos such as Hawaii and
Iceland (Klein and Dutrow, 2007). Basalt is a dark coloured extrusive (being exposed to
the cold atmosphere) igneous rock resulting in a fine-grained rock texture as opposed to
the coarser grained intrusive gabbro equivalent. Basalt is classified as a mafic rock due
to it being rich in magnesium (Mg) and iron (Fe) and poor in silica (SiO2) as opposed to
its felsic counterpart, Rhyolite, which is high in Si and alkali metals and poorer in Fe and
Mg. The common major mineral assemblages in Basalt are pyroxene (ortho- and
clinopyroxene) and calcium rich plagioclase such as anorthite. Olivine and augite are
also frequently present with olivine mostly as phenocrysts, and augite present as both
phenocrysts and the groundmass (Klein and Dutrow, 2007).
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A basaltic rock can be created from a mafic magma series which can be divided
into two possible groups viz., alkaline and subalkaline, where the subalkaline group is
further divided into tholeiitic and calc-alkaline basalt. The calc-alkaline series is mostly
restricted to complex convergent plate boundaries (Winter, 2001) although also
dominated by continental arcs (Tatsumi and Suzuki, 2009). Tholeiitic basalts are
typically generated at mid-oceanic ridges, intra-oceanic arcs and scattered intra-plate
volcanic occurrences, whereas alkaline basalts are constrained to intra-plate incidences
(Winter, 2001 and Tatsumi and Suzuki, 2009). A summary of the characteristics of
tholeiitic basalt from the subalkaline group and alkaline group can be seen below in
Figure 1.
Figure 1: Characteristic summary of Tholeiitic and Alkaline basalts (Winter, 2001).
The alkaline basalts are also characterized by a low silica content (silica-
undersaturated) and higher contents of alkalis such as sodium (Na2O) and potassium
(K2O) than the tholeiitic basalt series. The tholeiitic basalt series contain higher iron (Fe)
content whereas the calc-alkaline comprises of more magnesium (Mg) and alkalis
(Na2O+K2O) than tholeiitic basalt, as portrayed by the AFM diagram in
Figure 2.
The most distinct difference between tholeiitic and calc-alkaline magma series is
the redox state the magma has crystalized from. Tholeiitic magma is mostly formed from
a reduced magma state and calc-alkaline magmas from an oxidized state.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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Figure 2: AFM diagram showing element abundance between Tholeiitic and calc-
alkaline basalts (adapted from Winter, 2001).
This creates an excess of iron in the melt as iron poor minerals are depleted. The
oxidized state of a calc-alkaline melt produces enough magnetite (containing iron oxide)
to keep the iron content in the magma steady as it cools (Winter, 2001). Picritic basalt is
basaltic rock which contains high amounts of magnesium rich olivine as phenocrysts
together with pyroxene and augite.
The AFM diagram in
Figure 2 above portrays this formation of magnesium/iron rich minerals. As the
tholeiitic magma series cools and preferentially create Mg rich minerals, the Mg content
in the melt decreases. This results in the melt to progress to a higher iron concentration,
whereby Fe rich minerals are then preferentially created. After the iron content reserves
have also been exhausted the melt progresses to an alkali concentration to form alkali
rich minerals. In this process some Mg and Fe rich minerals get re-melted and get used
in the alkali mineral formation. In contrast to this, due to the calc-alkaline magma
precipitating magnetite, the ratio between Fe to Mg remains constant as they are depleted
evenly, therefore the melt concentration progresses in a straight line towards the alkali
corner. The preferential crystallization of magnesium rich silicate minerals can occur
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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within the tholeiitic melt if not re-melted. Tholeiitic and calc-alkaline rocks have been
found together indicating a differential fractional crystallization of a magma series to
create both rock types (Tatsumi and Suzuki, 2009).
2.2 South African Basalts
An account of most basalt appearances across South Africa in geological
chronology will follow. Significant occurrences of Groups/Subgroups/Formations will
be elaborated on where lesser or smaller Formations/Beds will only be mentioned.
The oldest account of a basaltic type rock in South Africa is in the Lower
Onverwacht Group, Barberton Supergroup and dates back 3 600 to 3 200million years
(Ma). These are referred to as komatiites (also termed komatiitic basalts) which are
similar to basalt although has different chemical compositions, noticeably a much higher
magnesium (Mg) content. These rocks were first discovered in the Komati River valley
east of Badplaas, Mpumalanga Province. The Upper Onverwacht Group overlays the
Lower Onverwacht Group and consists of basalt and dacite separated by a sedimentary
Middle Marker. These volcanic rocks as well as sedimentary rocks overlying them has a
dark green colour and are collectively referred to as the greenstone belt. In this specific
area it is termed the Barberton Greenstone Belt (BGB), situated south and southeast of
Nelspruit occupying and area of 120 x 50km (McCarthy and Rubidge, 2005 and Brandl
et al., 2006). The area south of the BGB has a number of greenstone belt fragments of
different sizes. Such as the greenstone belt fragment in northern Kwazulu-Natal
containing the Nondweni fragment/Group which created the southern boundary of the
Kaapvaal Craton 60km north of the Tugela thrust front. The Nondweni Group also
comprise of komatiitic basalt, basalt and basalt andesites in the Magongolozi and Witkop
Formations (Brandl et al., 2006).
The Nsuze Group of the Pongola Supergroup consists mainly of volcanic rocks
(basalt/andesite) which are interlayered with clastic sedimentary beds dating to around
3 074Ma (McCarthy and Rubidge, 2005 and Gold, 2006). A ~250m thick basalt layer is
present in the Crown Formation of the Jeppestown Subgroup from the West Rand Group,
as well as in the Bird Reef member of the Krugersdorp Formation in the Johannesburg
Subgroup from the Central Rand Group. They fall collectively under the Witwatersrand
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Supergroup which was dominated by sedimentation and contains mostly sedimentary
rocks. These rocks date back to approximately 2 910Ma (McCarthy and Rubidge, 2005
and McCarthy, 2006).
The extended sedimentation period of the Witwatersrand Supergroup was
terminated as a result of intense uplift which resulted in the rupture of the Kaapvaal
Craton. This uplift created large fractures to form in the crust leading to vast amounts of
very low viscous basalt to erupt and flow across the land surface, approximately 2 714Ma
(McCarthy and Rubidge, 2005). This created a unique volcanic-sedimentary supercrustal
record forming the Ventersdorp Supergroup. The majority of the extruded mafic lava
form part of the Klipriviersberg Group (the bottom section of the Ventersdorp
Supergroup) and is described as mainly tholeiitic basalts with a mild calc-alkaline
affinity. Komatiitic basalts are found at the base of the Klipriviersberg Group in the
Meredale Member of the Westonaria Formation (van der Westhuizen et al., 2006). At
2 700Ma the Zimbabwe Craton in the north and the Kaapvaal Craton in the south collided
creating the Limpopo Belt. As a result of this collision the Kaapvaal Craton developed
numerous fractures and fissures from where a bimodal assemblage of mafic and felsic
lavas poured. Before and between eruption events erosion and sedimentation were
dominant due to the elongated valleys created by the collapse of the highlands of the
Central Rand Group, this caused the development of the Platberg Group of the
Ventersdorp Supergroup. The basaltic and basaltic andesites are in minority in this group
compared to the more dominant rhyolitic and sedimentary rock sequences. The
Ventersdorp Supergroup ended with periodic eruptions of mafic lava creating the
Allenridge Formation of the Pniel Group (McCarthy and Rubidge, 2005 and van der
Westhuizen et al., 2006).
After a period of stability another crustal stretching and rifting event occurred
around 2 650Ma, leading to the deposition of sand and mud in these rifts with occasional
basaltic lava eruptions. This created the Wolkberg Group forming part of the Blyde River
Canyon. Thermal subsidence of the Kaapvaal Craton followed this new rifting event
whereby most of the landmass subsided below the sea level to create a new continental
shelf. This led to large deposits of sedimentation which created the Transvaal Supergroup
dominated by sedimentary and dolomitic rocks with occasional basaltic eruptions. These
eruptions include the Hekpoort formation containing basaltic andesite (rather better
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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known and termed the Hekpoort andesites) as well as tholeiitic basalt in the Silverton
Formation (McCarthy and Rubidge, 2005 and Eriksson et al., 2006).
The deposition of the Transvaal Supergroup ceased 2 060Ma ago and was
followed by the largest layered intrusion known in the world, namely the Bushveld
Igneous Complex (BIC). This volcanic event extruded a range of mafic to felsic lavas
creating three distinct components known as the Rooiberg Group, the Rustenburg
Layered Suite (RLS) and the Lebowa Granite Suite. The lowest unit of the Rooiberg
Group the Dullstroom Formation predominantly consists of basalt and basaltic andesite
which intruded and overlies the Pretoria Group. Near Stoffberg, Mpumalanga Province,
this formation is also present both above and below the Rustenburg Layered Suite. The
Dullstroom Formation is only basaltic to basaltic andesitic at the base and becomes more
felsic upward also containing pyroclastic and arenaceous layers. Basalt does not occur in
any other layers in the Bushveld Igneous Complex with the Rustenburg Layered Suite
primarily made up of a range of rock types such as dunite, pyroxenite, norite, gabbro,
anorthosite and magnetite to apatite rich diorite. These rocks are mostly the intrusive
equivalent of basalt with some chemical and mineralogical differences. The position of
the RLS in the central part of the BIC resulted in a longer time for the magma to cool and
therefore sufficient time for crystal growth. The Lebowa Granite Suite as the name
suggests is comprised of acid igneous rocks (McCarthy and Rubidge, 2005 and Cawthorn
et al., 2006).
A couple of hundred million years after the deposition of the Transvaal
Supergroup the Waterberg and the Soutpansberg Groups were deposited in an
environment showing first accounts of an atmosphere with free oxygen. This resulted in
the oxidation of the iron in the rocks to iron oxide creating a red colouration to the
sediments. The Waterberg Group predominantly consists of sedimentary rocks with some
interlayered granites from the Bushveld Igneous Complex as well as more mafic lavas in
the Nelspruit Subgroup (McCarthy and Rubidge, 2005 and Barker et al., 2006).
The lower units of the Soutpansberg Group contain more basaltic rock
occurrences which forms the Sibasa basalt Formation which erupted approximately
1 769Ma ± 34Ma ago with repetitive and cyclical eruptions, slightly exposed to air.
Therefore, zones of lenticular pyroclastic rocks are found in the basalt as well as
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
8
intercalations of clastic sediments laterally though the rock mass (Baker, 1979; cited in
Barker et al. 2006). The Sibasa basalts are described as dark green and massive with
zones of white amygdales, the rock usually is epidotised. According to Baker (1979; cited
in Baker et al. 2006) clinopyroxene and plagioclase are visible between the epidote,
chlorite and quartz matrix in less altered rocks. The Sibasa basalts are predominantly
volcanic rocks that reaches an estimated thickness of 3 000m, numerous lenticular
laterally persistent clastic sediment intercalations are also present. These clastic
sediments are mostly quartzite, shale and some conglomerate beds that reaches
thicknesses of 400m (Barker et al., 2006).
Further intercalated epidotized basalt layers between the sedimentary layers are
present in the overlying Fundudzi and Musekwa Formations of the Soutpansberg Group.
The Fundudzi Formation has an approximate 50m thick basalt layer and the Musekwa
Formation a 400m thick layer which are very similar to the Sibasa Formation although it
has individual layers that show a coarse gabbroic texture. These former two Formations
are only present and visible in the central and eastern Soutpansberg area (Barker et al.,
2006).
Approximately 190Ma ago the Karoo sedimentation was terminated due to
ruptures in the Earth’s crust when compression of the crust during the Karoo
sedimentation relaxed. This led to a large amount of basalt pouring out onto the Clarens
Formation that resulted in the Karoo Flood Basalt Province. The Karoo basalts are
mostly distinguished as the Drakensburg Group, although a second eruption event to the
east along the Mozambique border resulted in the Lebombo Group basalts (McCarthy
and Rubidge, 2005). The Drakensberg and Lebombo Groups constitute the uppermost
units of the Karoo Supergroup (McCarthy and Rubidge, 2005). The eruptions of the lava
mainly occurred from long fissures in the earth’s crust and flowed as massive sheets
typically between 10 to 20m thick. A large portion of the lava from the Lebombo Group
also consists of a felsic melt forming rhyolitic rock. Although the majority of the
Lebombo Group contain silica rich rocks there are still formations that are basaltic in
origin such as the Letaba, Sabie River and Movene Formations (from oldest to youngest).
The Drakensberg Group which constitute the main body of flood basalts covering
the Karoo sediments is made up of the Barkley East and Lesotho Formations (Duncan
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
9
and Marsh, 2006). The total thickness of the Drakensberg Group is approximately 1
400m, created by several rapid and successive low viscosity lava flows.
Olivine basalt is the dominant basalt type with different degrees of amygdale
content of non-amygdaloidal, moderately amygdaloidal (less than 10% amygdales) and
highly amygdaloidal types (Bell and Haskins, 1997). The individual lava flows are
mostly characterized by three zones, the basal, central and upper zone. The basal zone is
characterized with moderate to high amygdale content with distinctive pipe amygdales.
This formed as trapped gas in the lava progressed upwards due to the rapid cooling of
the basalt, when it made contact with the floor rocks on which it extruded, this formed
fine grained basalt. The central zone contains no or very few amygdales compared to the
basal and upper zones. This zone also has more time to cool which resulted in medium
to coarse grained basalt. The upper zone is again fine grained with the highest occurrence
of amygdales as well as volcanic glass due to rapid cooling on exposure to the
atmosphere. The flow contacts show very little weathering due to the rapid extrusion of
the various basalt flows following on one another (Bell and Haskins, 1997).
The Letaba Formation is described as picritic (olivine-rich) basalt, forming the
main mafic unit in the northern Lebombo area that thins out towards the 25° S line. The
Sabie River Formation overlies the Letaba formation from here with olivine-poor
tholeiitic basalt which extends southwards to the end of the Lebombo mountain range
west of Richards Bay, KwaZulu-Natal. Following these two dominant basalt units are
two silicic sequences of the Jozini and Mbuluzi Formations ending in the Movene basalt
Formation that has interbedded rhyolitic flows. The Movene Formation is confined to
Mozambique with a small portion present in northern Kwazulu-Natal just south of
Mozambique (Duncan and Marsh, 2006).
The inter-continental volcanic eruptions which created the Drakensberg and
Lebombo basalts and terminated the Karoo sedimentation only lasted approximately two
million years. Following this volcanic event most of South Africa experienced uplift in
conjunction with intense erosion, this removed large parts of the previously extensive
lava sheets. Although uplift dominated most of South Africa, a region in the central
Bushveld experienced subsidence which led to the preservation of the Karoo
sedimentation and volcanics, now known as the Springbok Flats Basin (McCarthy and
Rubidge, 2005).
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The Springbok Flats Basin is an extremely flat-lying section of the African
erosion surface which extends from Modimole (Nylstroom) to Mokopane (Potgietersrus)
(McCarthy and Rubidge, 2005). Outcrops are virtually absent in the exceedingly flat area
of the Springbok Flats Basin, therefore information on the stratigraphy of the basin was
mostly acquired from borehole data conducted by the Geological Survey (Johnson et al.,
2006). This borehole data indicates that the preserved Karoo basalts in the basin has a
maximum thickness of 460m in the north-eastern basin section and more than 750m in
the south-western basin section (Marsh, 1984).
The basalts of the Springbok Flats, according to SACS (1980; cited in Marsh,
1984), was originally correlated to the Letaba Formation of the Lebombo Group. This
name was collectively given to all basalts that were located below the rhyolites in
Lebombo. After additional investigations it was however found that the basalts of the
Springbok Flats were chemically and petrographically different to the Letaba Formation
basalts. From additional data presented by Marsh (1984) the Springbok Flats basalts more
closely associates to the Sabie River Formation and Lesotho Formation (the
Drakensberg’s Formation equivalent in Lesotho), although having a stronger supporting
correlation to the former.
2.3 Weathering of Basalt
The engineering properties of any rock or residual soil is dependent on the degree
and/or type of weathering the rock has undergone. Basalt is a basic crystalline rock,
consequently the rock can undergo chemical and physical weathering (decomposition
and disintegration) depending on the climate. Physical weathering is the process by
which a rock mass is broken down mechanically into smaller fractions of the original
rock material and eventually individual mineral grains. Through physical weathering the
fresh rock surface is exposed to the atmosphere to be influenced by chemical weathering
(Bih Che, 2012), if present in a climate which would induce chemical weathering. When
chemical weathering is dominant the mineralogy and chemistry of the rock material are
affected, creating mineralogical and geochemical changes, witnessed through textural
changes to the rock.
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These mineral and geochemical changes are achieved through a range of different
processes such as hydration, hydrolysis, oxidation, reduction, carbonation, dissolution,
leaching, precipitation and enrichment which leads to the formation of secondary
minerals which in turn reduces the strength of the rock. This is based on the principal that
minerals in an igneous rock that crystalized under high temperatures and pressures are
intrinsically unstable at the current atmospheric conditions. These minerals react readily
to change to more stable minerals such as clay minerals (Bih Che, 2012 and Paige-Green,
2007).
The chemical, mineralogical and physical properties of rocks change when
weathered, creating weaker material that is difficult to use as engineering material or to
engineer structures on (Moon and Jayawardane, 2004). This was observed with variation
in performance of weathered dolerite and basalt in road construction, due to the varying
degrees of weathering the rocks have undergone, as a result of different climatic
conditions (Weinert, 1980). Non-uniform weathering and redistribution of elements
result in the creation and accumulation of secondary (clay) minerals which create
heterogeneity in a rock mass or soil (Bih Che, 2012).
The different climatic environments and influences on the weathering of rock and
residual soil development is best represented by Weinert’s climatic N-value. This is
calculated from the total annual precipitation and maximum evaporation month in the
year (which usually is January in South Africa) times a factor of 12 to represent the year.
The N-value is calculated according to the equation below (Weinert, 1980):
N = 12.𝐸𝑗
𝑃𝑎 Equation 1
Where Ej = evaporation during January
Pa = annual precipitation
The most significant integers to regard for the N-value from this calculation is
N=1, N=2, N=5 and N=10. Where N>5 represents more arid areas with rainfall of
approximately less than 550mm per annum. More humid areas are represented by N<5
that has higher rainfall of approximately more than 800mm per annum (Weinert, 1980
and AFCAP, 2012).
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In very high humidity areas where Weinert’s climatic N value is less than 2, deep
residual soils would develop with a strong development of secondary minerals such as
smectite, notably montmorillonite, due to decomposition as the dominant mechanism.
Similar conditions are found in sub-humid areas where N is between 2 and 5 with a
decreased residual soil thickness compared to N<2 areas. Disintegration becomes more
influential as N approaches 5, with smectite minerals developing only after extended
weathering. In climatic areas where N>5 and approaching N=10 disintegration would be
dominant resulting in a thin residual soil cover, where decomposition of crystalline rock
would be insignificant, only a few secondary minerals would develop (Brink, 1979 and
Weinert, 1980).
Generalizing Weinert’s N-value, areas of N<5 tend to have higher concentrations
of iron and aluminium oxides, where areas of N>5 or approaching 5 have a higher
concentration of soil carbonates (Brink, 1979). As indicated above, rainfall is not the only
deterministic factor for the calculation of Weinert’s climatic N value, evaporation in the
area also plays a significant role.
Small areas exist, due to topography such as mountainous areas, with different
rainfall and evaporation conditions creating localized contrasting N values (Brink, 1979
and 1983 and Weinert, 1980). An area with a high rainfall and high evaporation will have
similar N-values to an area that has lower rainfall and low evaporation. Figure 3 indicates
the N=5 line in southern Africa with specific climatic N-values indicated.
The Drakensberg and Lebombo Group basalts in South Africa are located in areas
where the N-value is between 2 and 5 which implies that decomposition with a degree of
disintegration is present. As a result of the mountainous conditions of the Drakensberg,
intensive erosion is present preventing deep residual profiles to form but rather created
large exposures of fresh basalt, even though the climatic setting is favourable to chemical
weathering (Sumner et al., 2009). The annual precipitation is around 1000mm (Bell and
Haskins, 1997) indicating very low N-values. In lower relief and flat lying areas
decomposition creates deep soil profiles such as on the Springbok Flats with highly active
soils, this also occurs to a degree in the Lebombo Group basalts in the Kruger National
Park (Brink, 1983).
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When basalt is exposed to the atmosphere in environments closer to N=5 the rock
preferentially disintegrates to coarse-grained material and is associated with strong
development of calcretes (Brink, 1983).
Figure 3: Weinert’s climatic N-value, with N=2, N=5 and N=10 contour lines (adapted
from Weinert, 1980).
With the decomposition of a basic crystalline rock, such as basalt, the breakdown
and alteration of minerals will occur in conjunction with element exchange from the fresh
basalt rock to a residual soil throughout the profile. Houston and Smith (1997)
determined the degree of alteration of basalt by comparing a primary mineral in basalt to
a weathered product or secondary mineral in basalt from New South Wales Australia. In
their case using plagioclase feldspar (primary mineral) altering through decomposition
to smectite clay (secondary mineral). Moon and Jayawardane (2004) investigated the
Karamu basalts in New Zealand, and Hill et al. (2013) the basalts in northeast Ireland.
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The abovementioned found that after initial weathering, Fe-rich smectites are the
replacement product of weathered olivine and augite, and Al-rich smectites the
replacement product of weathered plagioclase. The study of Bih Chi et al. (2012) on
basaltic soils in humid tropic climates in south-western Cameroon, concentrated on the
weathering of olivine, pyroxene, amphibole and calcic plagioclase as the principal
minerals weathering from fresh rock to soil. These minerals forms first in the
crystallization process and therefore the most unstable minerals that readily reacts to
change compared to more stable minerals (Sumner et al., 2009). Bih Che et al. (2012)
portrayed the variable weathering trends of major elements in basaltic material in humid
climatic conditions, especially the alkali and alkali earth metals.
X-ray diffraction (XRD) is generally used to determine the secondary minerals as
it is a fast, accurate and cost-effective way of determining alteration minerals. XRD
spectra; a rapid semi-quantitative evaluation was used in the study of Houston and Smith
(1997). XRD is a widely used analytical technique to determine the type, amount and
textural distribution of altered or secondary minerals, such as plagioclase, olivine and
augite altering to smectite clay minerals. This is used in order to predict the engineering
quality of aggregates for use in road construction (Houston and Smith, 1997). The higher
the percentage of smectite present in basalt the less usable it will be as a building and
road aggregate, and residual soil will be less useful with an increase in plastic fines
content from the presence of smectite.
It is generally accepted and researched that the expansion of these Smectite Group
clays during the absorption of water is the main driving factor that deteriorates basic
crystalline material such as basalt (Paige-Green, 2007). In the basalts of the Karoo
Supergroup these clays or clay spots form as a result of deuteric alteration during the
cooling and crystallization of the melt. Deuteric alteration occurs where volatiles and
vapours from the magma are trapped immediately after or at the time of solidification in
the cooling rock mass. This results in the formation of volcanic glass and initiates the
alteration of the unstable primary minerals to change to secondary minerals. This is
especially relevant to active swelling clays and secondary minerals such as; zeolites,
chlorite, metallic oxides, montmorillonite and smectite clays (Bell and Haskins, 1997 and
Paige-Green, 2007).
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The volcanic glass, after formation, also start altering at an early stage to the
minerals listed above (Bell and Haskins, 1997, Paige-Green, 2007 and Sumner et al.,
2009). These secondary and clay minerals, specifically zeolite and metallic oxides, are
present in the Termaber basalt in Central Ethiopia. This was discovered during the
assessment of the rock mass for use as crushed aggregate and building stone (Engidasew
and Barbieri, 2014). With olivine and plagioclase feldspar as the first formed minerals
and therefore the most unstable minerals, they tend to be the minerals which alter first to
these secondary and clay minerals. Olivine in basalt tend to be limited due to this high
alteration to secondary minerals (Sumner et al., 2009). Engidasew and Barbieri (2014)
notes that an olivine basalt will be more altered than an olivine free basalt due to olivine
being more susceptible to alteration than augite. This can be attributed to olivine as a
high temperature mineral.
This early on alteration of the primary minerals to secondary and active clay
minerals is known as primary deuteric alteration. Secondary deuteric alteration occurs
much later when mineralizing fluids percolate through the solid rock and then
deuterically alter the remaining volcanic glass and primary minerals. This secondary
deuteric alteration can be witnessed and occurs at vesicular cavities and amygdales that
alters to these clay minerals (Bell and Haskins, 1997 and Sumner et al., 2009). These
weathered amygdales and altered glass patches in the rock create clay spots in the rock
mass which predominantly consist of montmorillonite (Bell and Haskins, 1997). Studies
conducted on the Karoo basalts during the Lesotho Highlands Water Project found that
montmorillonite is also the dominant replacing clay of olivine and plagioclase feldspar.
The latter appearing fresh although still contain alteration zones on the mineral grain
edges and cleavage plains in the form of montmorillonite (Sumner et al., 2009).
This all led to the now widely accepted fact that the main driving force that causes
basalt deterioration, is the volume changes associated with dehydration and hydration of
swelling clays and some zeolites present in the rock mass. This decreases the durability
of basalt for use as aggregate, building material and pavement construction (Bell and
Haskins, 1997).
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Apart from mineralogical alterations such as the percentage of secondary
minerals/clay content in a rock or residual soil, slight differences in terms of element
exchange or movement can indicate that weathering or alteration is taking place. An
indicator for slight weathering can be determined by the cation loss of a rock or soil
(Eggleton, 2001 cited in Moon and Jayawardane, 2004). In the early stages of basaltic
rock weathering the loss of Ca, Mg and Fe does not influence the change of mineralogy,
but rather changes the structure of the crystal lattice which will lead and result in
mineralogical changes (Moon and Jayawardane, 2004). The study conducted by Moon
and Jayawardane (2004) focused on stages of weathered basaltic rock.
During the common weathering trend, basalt experiences a loss of mobile
elements such as Mg2+, Ca2+, Na2+ and Fe2+ when transitioning from fresh basalt to a
weathered state as well as an Fe3+ increase (Moon and Jayawardane, 2004). This indicates
that in the initial processes of weathering iron oxidizes and basalt experiences a loss of
cations. Two stages of element exchange were noted by Moon and Jayawardane (2004)
viz. at the fresh to moderately weathered stage a rapid decrease in oxide concentrations
(CaO, MgO, FeO) occur followed by smaller changes from moderately weathered
onwards. Bih Che et al. (2012) displayed intense to complete decomposition of
plagioclase from signs of strong depletion of K2O, Na2O and CaO, the alkali and alkali
earth metals.
Liu et al. (1996, cited in Bih Che et al., 2012) as well as Bih Che et al. (2012)
noticed higher concentrations of Fe family elements (Ti, V, Co, Cr and Ni) in basalt
derived soils than the felsic counter parts. Bih Che et al. (2012) indicated that a greater
emphasis should be placed on using density measurements for mass balance equations.
This is to determine enrichment or depletion of an element, opposed to only relying on
relationships of element concentration between parent rock and soil. This was observed
by Bih Che et al. (2012) of elements that originally showed enrichment based on element
concentration relationships, where after the density of the soil and parent rock was
considered showed depletion of said element. This is due to a decrease in density from
parent rock to highly weathered rock to soil, as a result of altered minerals that changed
into secondary minerals. This leads to a progressive increase in porosity due to element
loss/transfer (Bih Che et al., 2012).
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As a result of utilizing the densities in the mass balance calculations, Fe and Al
are shown to be leached in certain horizons and not experience enrichment as most humid
tropic profile studies indicate. During the early phases of weathering, secondary minerals
such as non-swelling clays, hydroxides and goethite that can host Al2O3, Fe2O3 and TiO2
shows slight enrichment of these elements (Bih Che et al., 2012).
The study of Ameyan (1986) in northern Nigeria to determine the quality of land
facet mapping, used the coefficient of variance (CV) of their data (soil texture and cation
exchange capacity) in order to determine differences within a land facet and between
different land facets. Ameyan (1986) stated that there should exist a smaller variance of
the data within a land facet than between land facets in order to be grouped together or
indicate change in a dataset. Ameyan (1986) regarded a land facet or similar dataset
group as where the CV of a particular property is less than 33%. Whereby if it is greater
than 33% it would indicate a high enough variance and result to grouping the particular
property into a new land facet. The ranges of acceptable variance to land facets and
further soil classification and mapping are subjective and freely chosen. Although, the
effectivity of soil mapping or determination of the extent of change or variance of a
dataset is determined by the goals and objectives set out on what needs to be determined
and achieved (Ameyan, 1986).
Moon and Jayawardane (2004) determined an increase in trace element
concentrations in the initial weathering stages from fresh to moderately weathered basalt.
This could only be an apparent concentration increase that reflects the loss of Ca, Mg and
Fe instead of an inflow of trace elements into the system. The loss of the major elements
Ca, Mg and Fe are accompanied by the trace elements Rb and Sr, especially with Ca due
to similar ionic radii, therefore it is lost out of the system in similar manners. Bih Che et
al. (2012) also experienced Sr as the most mobile trace element in their study, relating it
to the decomposition of plagioclase. Sato et al. (1990, cited in Bih Che et al., 2012) as
well as Bih Che et al. (2012) noticed that the Fe2O3/MgO concentration decreased in the
rocks from Mt. Cameroon as the Ni and Cr concentrations increased, from fractional
crystallization model estimates. They also indicated that with an increase in weathering
the iron group elements would be enriched as silica, alkali and alkali earth metals get
depleted.
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It has been assumed that Yittrium (Y) is an immobile trace element in the
alteration and weathering of crystalline basalt. Although under extreme weathering
conditions with the formation of basalt derived laterites it is found that yittrium is leached
out and is mobile (Hill et al. 2013). In contrast to this Bih Che et al. (2012) noticed in
their study that with increased weathering intensity, Y progressively increased. Similarly,
they noticed that as weathering progresses most trace elements (Ba, Y, Zr, V, Ni, Co and
Ce) showed a relative enrichment, the most weathered sections having the highest
concentrations. Hill et al. (2013) noticed in their study that the Titanium (Ti) content
increases from fresh basalt to laterite formation, whereby it was previously considered
immobile during weathering. Zirconium (Zr) also follows a similar trend of increase
(assumed to be immobile) whereas Y concentrations decreases from fresh basalt to
weathered products. Similar to this, the study conducted by Bih Che et al. (2012) also
found mobilization of Ti and Zr from parent rock to residual soil, indicating that these
elements are not immobile.
2.4 Pedogenesis
Pedocrete formation is a prominent product from the continuous exchange of
elements and mineral alterations, through different weathering processes such as
disintegration, decomposition, hydrothermal alteration, diffusion etc. Taking place
together with continuous climate influences such as water table fluctuations, shallow
seepage water, rainfall intensity and evaporation rates. Pedocretes are a combination of
the in situ parent material and the different authigenic cement acquired through leaching
and then relatively concentrated (Brink, 1985). The authigenic cement for pedocretes
such as calcrete and ferricrete are formed when calcium carbonate (CaCO3) and iron
oxide (FeO) respectively are introduced into an existing soil, cementing or replacing the
in situ material. This is done by deposition through groundwater or from the soil
(AFCAP, 2012). Other pedocretes also include silcrete from silica, manganocrete from
magnesium, phoscrete from phosphate and gypcrete from gypsum deposition (Brink,
1985). Collectively ferricrete, calcrete and silcrete are known as duricrusts, pedocretes
or pedoderms are an important natural gravel group for the purpose of making roads
(McNally, 2003). The terms ferricrete, calcrete and laterite should predominantly only
be used if more than 50% of the pedocrete forming material is present (Brink, 1985).
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The iron rich fluid and deposited material that forms ferricrete and laterite is
focused around an Fe and Al sesquioxide-rich (Fe2O3+Al2O3) solution (McNally, 2003).
Ferricrete or ferruginous pedocretes are formed through two main processes viz. absolute
accumulation and relative accumulation, this also governs the formation of other
pedocretes. Absolute accumulation is focused around the addition of the sesquioxides to
the parent material. Whereas relative accumulation occurs when the soluble constituents
in the parent material are removed by intense weathering and free draining that results in
the sesquioxides to be concentrated. Even though these two processes usually occur
together at some degree one process is usually dominant (Brink, 1985). Indurated
ferricrete is predominantly formed through absolute accumulation from the upward,
downward or lateral transportation of iron (Brink, 1985).
Laterite is an iron rich horizon created by the in-situ breakdown and dissolution
of primary minerals with the removal of bases and silica, that got deposited in the
horizons above the breakdown. This term is usually given to tropical soils that underwent
advanced weathering (Brink, 1985 and Widdowson, 2003). Ferricrete differently to
laterites are dependent on the transportation of the material from another source. In this
study the term ferricrete will be collectively used for ferricrete and laterite, due to the
difficult determination of the constituent material origin, as a consequence of the flat
topography of the study sites (Widdowson, 2003).
Calcretes in South Africa are labeled by two processes viz. groundwater calcrete,
where carbonate is deposited above a fluctuating shallow perched or permanent water
table or lateral seepage of groundwater. The second process is pedogenic calcrete where
carbonate is leached by infiltrating rainwater through the upper horizons (AFCAP, 2012
and Brink, 1985). Although, most to all calcretes are part of the absolute accumulation
process (Brink, 1985). The geology or solid rock also determines if calcrete would form,
if the residual and/or transported soil is thin enough. If such a condition is present,
formation then most likely would occur above calcareous rocks such as limestone,
dolomite, calcareous shales and mudstones where calcium carbonate is leached out.
Calcrete formation is also possible with the release of calcium and magnesium above
basic rocks such as dolerite and basalt (AFCAP, 2012).
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A generalization made on Weinert’s climatic N-value to pedocrete formation is
that pedocretes in more arid, N=5 to N=10 climates in South-Africa, the western part of
the subcontinent, are more likely to be calcretes. Pedocretes in more sub-humid (N<5,
N=2) climates, the eastern and northern parts of the subcontinent, are more likely to form
ferricretes (Brink, 1979). This is due to the fact that reducing conditions mobilises iron
more readily, such as a wet season or high rainfall areas. The iron gets precipitated when
oxidizing conditions then occur e.g., when a dry season follows the wet season or high
evaporation occurs after heavy rainfall. At this point the calcium in the material would
already have been leached out and transported with this high degree of “wetness”, as
calcium is a readily mobile element (Brink, 1985). This can be interpreted that calcretes
tend to form more readily in low rainfall and high evaporation areas and ferricretes in
higher rainfall and lower evaporation areas. Netterberg (1969 and 1971 cited in Brink,
1985) stated that calcretes would predominantly form in areas with a rainfall less than
550mm. A good correlation for this statement would be the Weinert’s N=5 line for
calcrete formation representing arid conditions. A sub-humid climate N<5 would be
more favourable for ferricrete formation as stated above (Brink, 1985).
2.4 Engineering Geology
Basaltic rock is generally used as aggregate in concrete for building material and
road construction purposes. Certain calcretes that form in residual basalt above basaltic
rock are also used as road surfacing (Brink, 1983 and AFCAP, 2012). The durability of
basaltic rock as an aggregate is drastically affected by the decomposition a basic
crystalline rock usually undergoes. The integrity of material for use as a road aggregate
depends on the presence of certain alteration products in a weathered rock, such as the
increase of clay minerals with a high plasticity index (Houston and Smith, 1997 and
Brink, 1983). As described above the main driving force to secondary clay mineral
formation is a result of deuteric alteration. The durability of basalt is significantly
affected by the minerals created through deuteric action, which already occurs during the
solidification of a basic crystalline rock (Bell and Haskins, 1997). These clay minerals
are sensitive to water and have low shear strengths and reduces a pavement structure’s
durability.
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The construction of the Lesotho Highlands Water Project led to confirming the
presence of this deuteric alteration in the Drakensberg basalts and the influence it had on
the construction of the Katse Dam and transfer tunnel. Due to the presence of these
swelling clays on the mineral structure and clay spots in the rock mass, volume changes
occur when these clays are exposed to a change in moisture conditions. This results in
micro-fissuring, fissuring, jointing, fracturing and crazing to occur which increases the
porosity of the rock mass. The rate of disintegration is determined by the degree of
porosity created, strength of the rock and the distribution of active clay minerals (Sumner
et al., 2009).
Although, this process is self-perpetuating, as a result of the already formed
fractures/fissures in the rock mass which allows an increase in moisture to enter the rock
mass and reach the expanding clays. This in turn increases the fracture density and opens
new clay spot areas to an increase in moisture content which accelerates the rate of rock
disintegration (Bell and Haskins, 1997). This led to the transfer tunnel of the Katse Dam
to be completely lined by concrete instead of only partially, as well as the foundation
depth for the dam wall to be increased several meters due to the presence of extended
fractures (Bell and Haskins, 1997). This action of the active minerals is also dependent
on the texture of the parent rock. If the rock has a low permeability due to the rock texture
the active minerals won’t have such drastic effect on the strength and durability of the
rock. Whereby the mineralogy will not exclusively be sufficient enough to cause
deterioration of the rock for the design life of an engineering structure (Sumner et al.,
2009).
Van Rooy (1994, cited in Paige-Green, 2007) indicated that basalt material can
be considered suitable for concrete, road aggregate and rip-rap if less than 20% smectite
and 10% amygdales are present in the rock mass. Although, a more recent study
conducted by Paige-Green (2007) on durability testing for basic crystalline rocks to use
as road base aggregate had opposing results. Paige-Green (2007) noticed that the majority
of samples containing less than 20% smectite proved to be unsuitable for use as aggregate
based on additional testing such as, aggregate crushing value, durability mill index and
ethylene glycol testing. Paige-Green (2007) also noted that no deterioration occurred in
the samples containing amygdales during the ethylene glycol soaking test; which
accelerates the swell of the clay lattice. This indicated that more factors than just the
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22
mineralogy present in the rock mass affects the durability of the rock, such as the ease of
access available water has to the clay minerals.
This led to the notion that existing limit recommendations based on secondary
mineralogy which determines material durability is not completely refined. This
approach can’t exclusively be used to discriminate between minerals aiding in
degradation or aiding in performance (Paige-Green, 2007). The use of secondary
minerals in determining material durability for use as aggregate was refined by Paige-
Green (2007), it is indicated that materials can likely be durable for use as aggregate if
smectite content is less than 10%. Material would possibly be non-durable with smectite
greater than 10% if complemented with additional tests and compared to recommended
limits determined by Paige-Green (2007). These additional tests to be conducted when
the smectite content exceeds 10% are: Durability Mill Index, 10% Fines Aggregate
Crushing Value/Aggregate Crushing Value, Aggregate Impact Value and Ethylene
Glycol soaking test.
Due to the fine grained mineral structure of basalt it experiences a polishing effect
under traffic when used as a surfacing aggregate, it then does not adhere to bituminous
binders (Brink, 1983). Basaltic rock aggregate poses the risk of crumbling if it contains
nepheline which changes to analcime when exposed to the atmosphere, this mineralogical
change creates the crumbling of the aggregate (Brink, 1983).
Residual soils of basalt forming in areas where Weinert’s N-value is less than 5
contain active clays, especially in flat lying areas such as the Springbok Flats where
highly expansive decomposed basalt profiles occur (Brink, 1983). It is this expansive
component of the soils which creates problematic founding conditions.
Many pedocretes have a gap-graded material grain distribution as a result of
recemented, reworked and redepositional actions by alluvial, colluvial and groundwater
processes, creating an absence of coarse sand (McNally, 2003). Due to cavities created
after the processes of solution, redeposition and cementation, the particles of certain
pedocretes tend to have a porous structure.
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High liquid limits and plasticity indices in these materials are the result of
microporosity in the fines instead of excess clay minerals (McNally, 2003). It is due to
this porosity that unrippable indurated layers pose problems when blasted due to the
depressurization of the explosive gases through connected porosity (McNally, 2003).
Due to the high specific gravity of the hematite concretions created in a ferricrete
layer it can be compacted to a high density. As a result of this gravel content, surface
rutting can be counterattacked when unsealed. Most duricrust/pedocrete sheets and
boulders that are well-cemented are crushed and produce densely-graded road bases and
aggregate. Although, the dependability of the material can be suspect as well as the yield
of the coarse chips can be low (McNally, 2003). Base course crushed from calcrete can
pose problems of bitumen seal debonding as a result of salt presence or dust particles that
are incompatibly charged (McNally, 2003).
The properties of calcrete and specifically the range of engineering properties
calcrete can contain differ on the extent of cementation, which depends on varying
quantities of CaCO3. Calcrete can be a very hard material similar to limestone having
high cementation or have low cementation where the calcification is a soft powder in the
host material. In short summary, the calcrete types with increasing cementation are;
calcified soil, powder calcrete, nodular calcrete, honeycomb calcrete, boulder calcrete
and hardpan calcrete (AFCAP, 2012).
The geotechnical properties are significantly different for each calcrete category
due to different weathering properties, degree of cementation and the nature of the host
material (AFCAP, 2012). The degree of calcrete cementation is determined by factors
such as the environment and parent material present. In drier areas where Weinert’s N-
value is greater than 5, well developed calcretes that are useable in road construction will
be present, whereas in wet areas of N<2 calcretes would generally be absent (Brink,
1983). In sub-humid areas a range of calcretes would be able to form, although the
calcrete horizon would be too thin to excavate for road construction use (AFCAP, 2012).
The clay minerals that are most common in calcretes are palygorskite, montmorillonite
and seopilite. The most abundant clay mineral palyforskite has some unusual although
beneficial properties.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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It has a similar plasticity index to certain smectites but has a non-expansive lattice
and needle like shape instead of the typical flaky shape (AFCAP, 2012 and Brink, 1985).
Calcretes are useful as road construction material due to palygorskite having higher shear
strengths at similar moisture contents of other clays, a well as the low linear shrinkage
and dry densities (AFCAP, 2012). Calcretes have a range of engineering properties which
make it very useful in road construction such as having relatively low swell in respect to
high Atterberg Limits. This relates to having higher liquid limits and linear shrinkage in
relation to their Plasticity Index. Most calcretes have rather good CBR compaction and
low CBR swell despite having poor gradings and Atterberg Limits (AFCAP, 2012).
Brink (1983) provides tables of expected values for residual basalt of the
Drakensberg Formation in Lesotho (valley and mountainous settings) and the Letaba
Formation of the Lebombo Group in Komatipoort, from previous investigations. Typical
values for the residual basalt for the Sibasa basalt Formation from the Nzhelele dam in
Venda is provided in Brink (1981). Averages of these formations and settings area
summarised in Table 1. A valley setting in Lesotho is considered below 2 500m and a
mountainous setting above 2 500m:
Table 1: Expected Average values of Residual Basalt for Drakensberg, Sibasa and Letaba
Formations, Brink (1981 and 1983).
Formation Setting /
Location
Percentage
passing
0.075mm
Atterberg Limits Mod ASSHTO CBR VALUES at% Mod.
AASHTO
Plasticity
Index
(PI)
Liquid
Limit
(LL)
Linear
Shrinkage
(LS)
MDD
(kg/m3)
OMC
(%) 90% 93% 95%
Drakensberg Valley 9.7 13 38.8 7.7 2060 10.3 18 24.9 29.3
Mountainous 14.2 11.4 37.5 5.7 967.6 13.3 11.9 18.5 24.3
*Sibasa Nzhelele Dam 16 14.5 50.5 6 - - - - -
Letaba Komatipoort 40 18 40 9.5 1996 12.5 - - 45 MDD – Maximum Dry Density; OMC – Optimum Moisture Content, PI – Plasticity Index
*Brink (1981) indicates the values are similar to the Sibase area but somewhat drier.
The valley and mountain settings display similar values in all aspects from the
Atterberg Limits to the compaction characteristic.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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3. CASE STUDY
This research study focuses on 5 sites chosen based on data availability, locality
and opportunity. These sites are: the northern basalt (Mooiplaas) and southern basalt
(Nhlowa) supersites in the Kruger National Park (KNP) where an opportunity existed to
investigate undeveloped and undisturbed landscape. This also provided the prospect to
be part of the well-established and growing research community of the KNP in
contributing to a collective data set for different disciplines. It also provided a large study
area, these two sites forming the main focus of the research. The remaining sites are at
Siloam (Soutpansberg) and Roedtan (Springbok Flats) which are smaller and more
concentrated in respect to size and data points. These two sites were available from
previous personal shallow soil site investigations. The Codrington site was investigated
as another frame of reference for the Springbok Flats basalts and to extrapolate the data
from the Roedtan site. A more specific description on the individual site’s climate and
geology follows.
3.1 KNP Supersites
3.1.1 Supersite background
The selection of the supersites in the KNP was done by a group of SANpark
scientists as well as research collaborators from outside the park. The general selection
of the sites was based on catchment boundaries so that arbitrary boundary shapes could
be avoided. This was also decided since the availability of water spatially and temporally
constrains ecological processes (Smith et al., 2013). Many of these ecological processes
play out on a template created by patterns of geology, climate, morphology, soils and
vegetation which would control water fluxes. These patterns are mostly tied together in
semi-arid climates found in the KNP (Smith et al., 2013).
An example of this is that at certain hillslope positions, catenas of soil and
associated vegetation are found, which creates sequences that reflects patterns of water
availability within a sub-catchment (Smith et al., 2013). Areas with similar climate,
geology and morphology create repeated sequences of these catenas which produces
physiographic zones or land systems (Venter, 1990 cited in Smith et al., 2013).
Catchment/sub-catchment boundaries and catenal elements were used to delineate
research and monitoring sites within distinct physiographic zones (land systems),
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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The aforementioned, allowed sites to be placed within an eco-hydrological
context that controls many ecological processes. The more specific criteria for selecting
the supersites were based on the following as stipulated in Smith et al. (2013):
1. That the sites should cover the two main abiotic variables that create the large scale
differences in the park viz. the geology which would be granite and basalt as well as
rainfall intensity with higher rainfall in the south and lower in the north.
2. Furthermore, the sites should be large enough so that at least one 3rd order
catchment/river occur solely on a single geology type. This allows studies to take
place at three different scales viz. primary, secondary and tertiary streams.
3. The sites should also include the soil patterns (catenal sequences) and hillslope
vegetation that normally occurs in the local land system.
4. The sites should be easily accessible from as many sides as possible
5. They should be located near research camps and facilities.
6. Be outside areas demarcated as “Wilderness” or “Remote” in the KNP zoning plan,
in order to allow installation of instrumentation.
Based on criteria 4 – 6 the main boundaries of the supersites are formed mostly
by roads, and that a single order catchment may be too small or difficult to access for
certain study types. Therefore, the sites were outlined larger than the catchment itself,
where the sub-catchment should become the focal point of research (Smith et al., 2013).
The KNP was divided by Venter (1990), into 11 land systems based on the
similarities in landforms and hillslope sequences of soils, and dominant woody and
herbaceous vegetation on a 1:1 000 000 scale. These land systems were further sectioned
into 56 land types at a 1:250 000 scale; see Figure 4 for representation. The two southern
supersites chosen, occur within two of the four largest land systems which make up 40%
of the total park area. As indicated by Figure 4: the southern granite supersite is part of
the Skukuza land system and Renosterkoppies land type with the southern basalt
supersite part of the Satara land system and Satara land type, both receives relatively high
rainfall. The northern supersites receive less rainfall than the southern supersites (Venter
1990, cited in Smith et al., 2013). The northern granite supersite is part of the Phalaborwa
land system and Shivhulani land type and the northern basalt supersite is part of the
Letaba land system and Mooiplaas land type (Venter 1990, cited in Smith et al., 2013).
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Figure 4: Supersites, Land Types and
Land Systems of the Kruger National Park
(Smith et al., 2013, originally adapted from
Venter, 1990).
Mooiplaas
Northern Basalts
Ngwenyeni
Northern Granites
Stevenson-Hamilton
Southern Granites
Nhlowa
Southern Basalts
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3.1.2 Geology ― Mooiplaas and Nhlowa
The northern basalt (Mooiplaas) and southern basalt (Nhlowa) Supersites are
respectively underlain by basaltic bedrock of the Letaba Formation and Sabie River
Formation of the Lebombo Group (Duncan and Marsh, 2006), Figure 7. The western
portion of the Nhlowa site is underlain by a narrow slice of sandstone from the Clarens
Formation, Karoo Supergroup (Barberton, 1986). This portion is approximately 962ha
(26.92%) of the site and is portrayed in Figure 5 below. The north-western corner of the
Mooiplaas site is underlain by the Goudplaats biotite gneiss, Timbavati olivine gabbro
and sandstone, which constitutes 1 574ha (13.85%) of the total surface area of the site
and is portrayed in Figure 6 below (Tzaneen, 1985).
Figure 5: Geological map overlay of the Nhlowa research supersite (©Google Earth,
2015 and Barberton, 1986).
The Lebombo basalts are collectively labelled as the Letaba Formation basalt
according to the published 1:250 000 Geological map, sheets 2530 Barberton, and
described as green, fine grained mafic lava, locally porphyritic, amygdaloidal in places
and interlayered with rhyolite near the top.
Site Boundary
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Figure 6: Geological map overlay of the Mooiplaas research supersite (©Google Earth,
2015 and Tzaneen, 1985).
Both the northern and southern basalt landscapes are topographically
characterized by flat to moderately undulating plains. This is a result of the near
horizontal lava flow sheets as well as the ease with which the mafic lavas decompose
(Venter, 1990). As a result, the soil profiles across a site do not differ as extensively as
for example on the granite sites that contain more pronounced land forms such as hills
and valleys.
3.1.3 Southern Basalt Research Supersite (Nhlowa)
The Nhlowa site is situated approximately 10km south of the Lower Sabie rest
camp. The site is bounded by three public dirt roads for the eastern, northern and western
boundaries, and one private dirt road as the southern boundary, depicted in Figure 8. The
site is approximately 3 573ha in size. The 1:50 000 Topographical map, sheets 2531 BA
and BB Mpumalanga, indicate that the site contain three river systems flowing through
the site to the north-east. Along the northern boundary is the Shimangwana River,
through the middle of the site is the Nhlowa River. Along the eastern boundary flowing
north is the Nhlanganzwane River, all three rivers are ephemeral/non-perennial streams.
Site Boundary
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Figure 7: Lebombo Group distribution and supersite localities (Duncan and Marsh,
2006).
Figure 9 below shows a graphical representation of the stream orders and
boundaries of the Nhlowa site that occurs in the Satara land type. This area is
characterized by shallow to moderately deep red olivine-poor clays according to Smith
et al. (2013) and is found to be very flat with open tree savannah. The flat to moderately
undulating plains being a result of the mafic lavas weathering easily (Venter, 1990).
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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The Nhlowa site has a maximum gradient of 0.39 degrees from the south western
corner to the north eastern corner (© 2015 GoogleEarth), representing a change in
elevation of approximately 60m over 8 666 m.
The southern supersites receive more rainfall than the northern supersites
according to Smith et al. (2013), the average rainfall for the Nhlowa site is
610mm/annum. This was measured through long term rainfall at Crocodile Bridge
approximately 13km from the Nhlowa site center between 1940-1941 and 2010-2011.
Figure 18 indicates that the Nhlowa site is located in an area with a mean annual
evaporation of between 1600-1700mm (Middleton and Bailey, 2008, based on the
WR2005 map). The conceivable calculated Weinert’s climatic N-values, based on the
range of rainfall and evaporations, according to Equation 1 in Chapter 2.3 are:
With 1600mm mean annual evaporation:
N-value = 2.62
With 1700mm mean annual evaporation:
N-value = 2.78
From these calculated N-value the Nhlowa site is located in the N-value range of
between 2 and 5, classified as a sub-humid area (Brink, 1979).
Figure 8: Site boundary and auger hole positions: Nhlowa research supersite on the
Southern Basalts (©Google Earth, 2015).
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Figure 9: Stream orders: Nhlowa research supersite on the Southern Basalts (as depicted
in Smit et al., 2013).
3.1.4 Northern Basalt Research Supersite (Mooiplaas)
The Mooiplaas site is located approximately 1.40km north-east of the Mopani
Rest Camp from the site’s western boundary. The Mooiplaas site, at 11 368ha, is much
larger than the Nhlowa site. The boundaries of the site are also formed by public dirt
roads along the northern, southern and western boundary with the H1-6 Mopani-
Shingwedzi tar road as the western boundary, depicted in Figure 10 below.
As mentioned above the Mooiplaas supersite is situated within the Mooiplaas
land type and according to Smith et al. (2013) is characterized by dark olivine-rich soils.
The site has very low stream density as well as very flat topography. The Mooiplaas site
has a maximum gradient of 0.20 degrees from the north western corner to the south
eastern corner, representing a drop in elevation of approximately 60m over 17 000m.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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The Mooiplaas site has the Mabohlelene river system (a 2nd order river) in the
north-western corner of the site flowing south-west, eventually flowing into the Tsende
River. The Shipandani 1st order stream on the western boundary of the site flows south
south-east, with the Mooiplaas 1st order stream in the middle of the site flowing south
which also flows into the Tsende River. The Tsende River flows south-east and
eventually south outside the site boundary. Here the Tsende River joins with the Nshawu
River on the eastern border of the site flowing south as well. Figure 11 portrays the rivers
in and around the site (1:50 000 Topographical sheet 2331 AD and CB).
The northern supersites receive less rainfall than the southern supersites
according to Smith et al. (2013), the average rainfall for the Mooiplaas site is
480mm/annum. This average was determined through long term rainfall measurements
approximately 5km from the Mooiplaas site center between 1940-1941 and 2010-2011.
Figure 18 indicates that the Mooiplaas site is possibly located across two areas with
different evaporation rates divided along north-east south-west. The mean annual
evaporations of these areas are 1700-1800mm and 1800-1900mm (Middleton and Bailey,
2008, based on the WR2005 map).
The conceivable calculated Weinert’s climatic N-values, based on the range of
rainfall and evaporations, according to Equation 1 in Chapter 2.3 are:
With 1700mm mean annual evaporation:
N-value = 3.54
With 1800mm mean annual evaporation:
N-value = 3.75
With 1900mm mean annual evaporation:
N-value = 3.95
The large evaporation range indicated no significant difference to the calculated
N-value. According to the calculated climatic N-values, the Mooiplaas site is located in
the N-value range of 3.54 to 3.95 which would be classified as a sub-humid to slightly
arid areas with N<5. These values indicate that the Mooiplaas site is a drier area than the
Nhlowa site with higher evaporation and lower rainfall.
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Figure 10: Site boundary and auger hole positions: Mooiplaas research supersite on
Northern Basalts (©Google Earth, 2015).
Figure 11: Stream orders: Mooiplaas research supersite on Northern Basalts (as depicted
in Smit et al., 2013).
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3.2 Siloam site
3.2.1 Site description
The original investigation at Siloam on the Sibasa basalts was to conduct a
shallow soil engineering geological investigation for the proposed new residential
extensions and road construction at the Siloam hospital. The site is situated in the Siloam
area south of the R523 (Musina road), it is located approximately 30km from the N1
highway on the R523 towards Thohoyandou, see Figure 12 for view of site.
The site is mainly covered with natural grass and small to medium size shrubs
and larger trees and has a size of 9.17ha (91 691m2). The general slope direction is
towards the south to south-east with an elevation difference of 832mamsl (meters above
mean sea level) to 815mamsl. This represents a drop in elevation of 17m over
approximately 400m which gives an average slope of 5% to 6% or approximately 3° (©
2015 GoogleEarth). A branch of the Mutangwi river system is located approximately
60m south-east from the site. This river flows south-west into the Nzhelele River system
approximately 820m south of the site which in turn flows west North-west.
A small drainage channel from the mountain is also present approximately 260m
west of the site flowing into the Nzhelele River (1:50 000 Topographical sheet, 2330
CC). Numerous valleys formed in the Soutpansberg due to the headwaters of the Nzhelele
and Pafuri rivers cutting through the quartzites. Two of these valleys that have formed
divide the Soutpansberg into three mountain ranges and valleys where Siloam falls within
the first valley between the first two mountain ranges (SoER, 2004).
3.2.2 Rainfall and evaporation
High rainfall of more than 2 000mm occur in the eastern areas of the
Soutpansberg between Louis Trichardt and the Kruger National Park. The northern and
western areas receive much less rainfall of between 200mm and 300mm. The site on the
Sibasa basalts are located north of the R523 in the town Siloam which places the site in
the high rainfall section of the Soutpansberg. As a result of such high rainfall these basalts
have varying weathering depths which can extend from approximately 2m to 3m to 20m
with fresh rock and core-stones present from shallower depths (Brink, 1981).
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Figure 12: Site boundary and test pit positions: Siloam site on Sibasa Basalts (©Google
Earth, 2015).
Thohoyandou is approximately 30km from Siloam and the closest town that has
research and measured data pertaining to the Soutpansberg climate. This would therefore
be the closest representation to the climate at Siloam. Figure 17 below shows that Siloam
and Thohoyandou fall approximately in similar mean annual precipitation ranges, with
Thohoyandou in the 800-1000mm/annum and Siloam between the 600-800mm/annum
and 800-1000mm/annum range. According to the data gathered for the Limpopo State of
the Environment Report (SoER, 2004), the average rainfall in Thohoyandou for the
period of 1982-1990 was 679mm and for the period of 1997-2003 was 810.63mm,
portrayed in Table 2 below (SoER, 2004).
Figure 18 indicates that the Siloam site is also on the border of two areas with
different evaporation rates. The mean annual evaporations of these areas are 1300-
1400mm and 1400-1500mm (Middleton and Bailey, 2008, based on the WR2005 map).
The conceivable calculated Weinert’s climatic N-values, based on the range of
rainfall and evaporations, according to Equation 1 in Chapter 2.3 are:
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
37
With 1300mm mean annual evaporation and 679mm rainfall:
N-value = 1.91
With 1300mm mean annual evaporation and 810mm rainfall:
N-value = 1.60
With 1400mm mean annual evaporation and 679mm rainfall:
N-value = 2.06
With 1400mm mean annual evaporation and 810mm rainfall:
N-value = 1.73
With 1500mm mean annual evaporation and 679mm rainfall:
N-value = 2.21
With 1500mm mean annual evaporation and 810mm rainfall:
N-value = 1.85
The Siloam site falls in the N-value range of 1.60 to 2.21 which would be
classified as a sub humid area N<5 to humid area N<2 (Brink, 1979).
3.2.3 Geology
The Sibasa basalt Formation at Siloam forms part of the Soutpansberg Group
which erupted approximately 1769 ± 34 Ma ago with repetitive and cyclical eruptions,
slightly exposed to air (Baker, 1979 cited in Barker et al. 2006). Therefore, zones of
lenticular pyroclastic rocks are found in the basalt as well as intercalations of clastic
sediments laterally through the rock mass (Baker, 1979 cited in Barker et al. 2006). The
Sibasa basalts are described as dark green and massive with zones of white amygdales
where the rock is usually epidotised. According to Baker, 1979 cited in Baker et al. 2006,
clinopyroxene and plagioclase are visible between the epidote, chlorite and quartz matrix
in less altered rocks.
The Sibasa basalts are dominantly volcanic rock and reaches an estimated
thickness of approximately 3000m. Although numerous lenticular laterally persistent
clastic sediment intercalations are also present. These clastic sediments are mostly
quartzite, shale and some conglomerate reaching thicknesses of 400m (Barker, 2006).
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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According to the published 1:250 000 Geological map, sheet 2230 Messina, the
Sibasa basalt deposit is described as; basalt with minor tuff, sandstone, quartzite and
shale; see Figure 13 for geological map.
Figure 13: Geological map overlay of the Siloam site (©Google Earth, 2015 and
Messina, 1981).
3.3 Roedtan and Codrington
3.3.1 Site description
The investigation that was conducted at Roedtan was for a shallow soil
engineering geological assessment for the construction of a proposed Police Station. The
site is located on the eastern side of the N11 highway 400m south of Roedtan, see Figure
14.
The site is covered in long natural grass with minor shrubs and small to medium
sized trees across the site. The site is fairly flat with an elevation difference of 975mamsl
to 972mamsl across the 3.57ha (35 717 m2) site (© 2015 GoogleEarth). The site is located
in a low relief area with no large prominent hills or mountains in a radius of
approximately 26km. The nearest pronounced drainage feature or river is the Olifants
River approximately 40km east from the site.
Approximate
site location
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The only visible drainage feature near the site is a small stream approximately
1.80km north of the site flowing south east (Topographical map, sheet 2429 CA and CB).
Figure 14: Site boundary and test pit positions: Roedtan site on Springbok Flats Basalts
(©Google Earth, 2015).
The data at the Codrington site was taken from an open quarry located on the
R576 road to the R101 road to Codrington. The quarry is approximately 2km from the
N1 on-ramp to Codrington along the R576 west and 400m east of the R101.
The site is fairly flat with no prominent hills or mountains in a radius of
approximately 20km. The Langkuilspruit is located approximately 2.70km north-west of
the site flowing in a western direction. Larger rivers such as the Platrivier (Utsane) is
located approximately 9km west of the site flowing south South-east and the
Pienaarsrivier approximately 16km south from the site flowing west. The Codrington site
in contrast to the Roedtan site has much more small streams and dams located around it
in an roughly a 4km radius (Topographical map, sheets 2528 AB and AA).
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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Figure 15: Codrington site on Springbok Flats Basalts, approximate area of investigated
quarry (©Google Earth, 2015).
3.3.2 Rainfall and evaporation
Mokopane (Potgietersrus) is situated approximately 50km north along the N11
from Roedtan and is the closest town with research data to represent the environment and
climate in the area (the Limpopo State of the Environment Report, 2004). Figure 17
below shows that Roedtan, Mokopane as well as Polokwane falls roughly in the same
mean annual precipitation range of 400-600mm/annum. Mokopane possibly also falls
within the 600-800mm/annum range. Table 2 below indicates Mokopane had an average
rainfall of 344.18mm for the period of 1996-2003.
Polokwane had an average rainfall of 472.86mm for the period of 1993-2003 and
478mm for the period of 1961-1990 (SoER, 2004). The website SAexplorer indicates
that Roedtan receives roughly 443mm per year the highest rainfall occurring in December
with 93mm (SAexplorer, 2000-2014). Figure 18 indicates that the Roedtan site is located
in an area with a mean annual evaporation of between 1800-2000mm (Middleton and
Bailey, 2008, based on the WR2005 map).
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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The conceivable calculated Weinert’s climatic N-values, based on the range of
rainfall and evaporations, according to Equation 1 in Chapter 2.3 are:
With 1800mm mean annual evaporation and 400mm rainfall:
N-value = 4.5
With 1800mm mean annual evaporation and 600mm rainfall:
N-value = 3.00
With 2000mm mean annual evaporation and 400mm rainfall:
N-value = 5
With 2000mm mean annual evaporation and 600mm rainfall:
N-value = 3.33
The Roedtan site falls in the N-value range of 3.00 to 5.00 which would classify
as a sub humid to slightly arid area (N<5). With the highest calculated value of N=5, the
site would be considered to tend more to an arid climate area (Brink, 1979). According
to Figure 3 Roedtan is located between the N=5 and N=2 lines displaying the accuracy
of the calculated values.
Bela-Bela (Warmbaths) is approximately 18km north from Codrington which is
the closest town with measured rainfall data in the Limpopo State of the Environment
Report (2004). According to SoER (2004) the average annual rainfall in Bela-Bela for
the period of 1961-1990 was measured at 634mm. According to Figure 17 Bela-Bela is
located in the mean annual precipitation range of 600-800mm which supports the
measurements. Although Codrington is located more in the 400-600mm mean annual
precipitation range it is close to the 600-800mm range.
The mean annual precipitation measurement of 634mm is then interpreted as a
maximum possible value for Codrington and 400mm the minimum. Figure 18 indicates
that the Codrington site is located in an area with a mean annual evaporation of between
1700-1800mm (Middleton and Bailey, 2008, based on the WR2005 map).
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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The conceivable calculated Weinert’s climatic N-values, based on the range of
rainfall and evaporations, according to Equation 1 in Chapter 2.3 are:
With 1700mm mean annual evaporation and 400mm rainfall:
N-value = 4.24
With 1700mm mean annual evaporation and 634mm rainfall:
N-value = 2.68
With 1800mm mean annual evaporation and 400mm rainfall:
N-value = 4.50
With 1800mm mean annual evaporation and 634mm rainfall:
N-value =2.84
The area of Codrington falls in the calculated N-value range of 2.68 to 4.50,
which would classify as a sub humid to slightly arid area (N<5) (Brink, 1979). According
to Figure 3, Codrington is located between the N=5 and N=2 lines, closer to the N=5 line,
which would indicate the values of N=4.5 to 4.24 more likely values.
3.3.3 Geology
The inter-continent volcanic eruptions which formed the Drakensberg and
Lebombo basalts and stopped the Karoo sedimentation only lasted approximately two
million years. Following this volcanic event most of South Africa experienced uplift in
conjunction with intense erosion removing large parts of the previously extensive lava
sheets. Although uplift dominated most of South Africa, a region in the bushveld
experienced subsidence which led to the preservation of the Karoo sedimentation and
volcanics, now known as the Springbok Flats basin (McCarthy and Rubidge, 2005).
The Springbok Flats Basin is an extremely flat section of the African erosion
surface which extends from Modimolle/Nylstroom to Mokopane/Potgietersrus
(McCarthy and Rubidge, 2005). Outcrops are extremely scarce in the exceedingly flat
area, therefore information on the stratigraphy of the basin was mostly acquired from
borehole drilling conducted by the Geological Survey (Johnson et al., 2006). These
borehole data indicate that the preserved Karoo basalts in the basin has a maximum
thickness of 460m in the north-eastern section and more than 750m in the south-western
section (Marsh, 1984).
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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The basalts of the Springbok Flats according to SACS, (1980 cited in Marsh,
1984), was originally correlated to the Letaba formation of the Lebombo Group. This
name was collectively given to all basalts that were located below the rhyolites in
Lebombo. Although after additional investigations it was found that the Springbok Flats
were chemically and petrographically different to the Letaba Formation basalts.
Additional data presented by Marsh (1984) indicate the Springbok Flats are more
closely associated to the Sabie River Formation and Lesotho Formation, although having
a stronger supporting correlation to the former. See Figure 16 below for geological map
representation.
Figure 16: Geological map overlay of the Roedtan and Codrington site on the Springbok
Flats, (©Google Earth, 2015, Nylstroom, 1978 and Pretoria, 1980).
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
44
Figure 17: Mean annual precipitation across Limpopo Province (SoER, 2004).
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
45
Figure 18: Mean Annual evaporation of reasearch sites (WR2005 map overlay to
©Google Earth, 2015).
Table 2: Total Annual Rainfall data for selected towns in Limpopo.
Year
Mokopane in
(mm/annum)
Polokwane in
(mm/annum)
Thohoyandou in
(mm/annum)
1993 * 356.30 *
1994 * 381.60 *
1995 * 678.00 *
1996 797.60 869.40 *
1997 470.40 584.80 415.40
1998 366.00 438.20 722.80
1999 379.20 368.80 872.00
2000 456.60 637.40 1968.20
2001 98.80 480.60 1004.20
2002 132.00 254.60 362.40
2003 52.80 151.80 329.40
Average (mm) 344.18 472.86 810.63
Avr. 1962-1990
(mm rainfall) * 478.00
(1982-1990)
679.00
*Data not available/measured
(Table adapted from Limpopo State of the Environment, 2004)
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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4. METHODOLOGY
4.1 Desk study procedure
The basic site investigation procedures as outlined in SANS 634 2012:
Geotechnical Investigations for Township Development was followed in the
investigation of the sites. This procedure was followed in order to cover all relevant
aspects of the site and have a structure to the investigation that is tested and proven to
work. The Mooiplaas and Nhlowa sites in the KNP had 1:10 000 orthographic
photographs available that were studied, along with the 1:50 000 topographical maps of
sheets 2331 AB, CB and sheets 2531 BB, BD respectively. The 1:250 000 published
geological maps, sheet 2330 Tzaneen were used for the Mooiplaas site and sheet 2530
Barberton was used for the Nhlowa site. These were used in conjunction with the other
maps in order to determine all possible structures on the sites before the field work was
conducted.
This allowed for more precise planning on auger hole excavation, focusing on
different land facets. Due to the size of the KNP sites the land facets that were focused
on were hill crests, hill midslopes and footslopes. Although as a result of the extremely
flat slopes on site (due to the nature of how the basalts were deposited and weathered)
differences in these land facets was problematic to determine on the topographical map
and the naked eye on site. The contour lines on the topographical map were spaced so far
apart that distinct hill- crests, -midslopes and -footslopes could not be effectively
identified and merge together. This was also noticed on site trying to distinguish the slight
rise and fall of the slopes with the naked eye. This resulted in a large decrease in accuracy
to the land facet system. As a result of this, the system became ineffective and primary
use of the system had to be abandoned. The land facet system still provided guidance
together with the information on stream flow in the area and professional judgement to
determine auger positions.
The same desk study investigative structure described above was used with the
Sibasa basalts at Siloam and the Springbok flats basalts at Roetan and Codrington. For
the Sibasa basalts the 1:50 000 Topographical map, sheet 2230 CC, together with the
1:250 000 published Geological map, sheet 2230 Messina, was used to analyse the
possible geomorphological environment.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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For the Springbok flats basalt at Roetan the 1:50 000 Topographical map, sheet
2429 CA and 1:250 000, sheet 2428 Nylstroom was used. For Codrington the 2528 AB
sheet of the 1:50 000 Topographical map and the 2528 Pretoria sheet of the 1:250 000
Geological map was used. Only one data point at the quarry at Codrington was gathered
in order to provide extrapolative data for Roetan. Due to the smaller sizes of these sites
focus was not placed on land facets and major structures across site. Emphasis was on
investigating as much of the site as possible and not to overlook important soil
development characteristics of the basaltic site. The difficulties and problems
experienced with the KNP sites would only increase with the decrease in size of the sites.
Where the contour lines on the topographical map were spaced so far apart that the
distinct hill- crests, -midslope and –footslope land facets were not found together on the
small sites.
4.2 Field work procedure
Due to the pristine conditions of the supersites in KNP, large machines such as a
tractor loader backhoe (TLB) could not be utilized to excavate test pits for soil profile
descriptions or sampling. The investigations at the Mooiplaas and Nhlowa sites were
therefore conducted using a hand auger to excavate, sample and describe the soil profile.
The effective description of the soil profile with the use of a hand auger was concerning
at first. Although Botha and Porat (2007) portrays the successful use of a hand auger
down to 6m for the description of soil profiles in dunes on the southeast African coastal
plains in Maputaland, South Africa. Similarly, more recently, Connallon and Schaetzel
(2017) successfully sampled and described the Chippewa river delta of Glacial Lake
Saginaw in central lower Michigan, USA, with the excavation of 180 auger holes with a
2m long auger.
Therefore, a hand auger with a 1 m long shaft and bucket dimensions of 12 cm in
diameter and 22 cm long was used. The depth of the auger holes was limited to the type
and extractability of the material encountered. At the research supersites in KNP the hand
auger could not excavate through the highly weathered basalt horizon and mostly refused
in this horizon. This shallow refusal was not a critical problem as information down to
the highly weathered basalt was sufficient for the study.
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As a result of this fact the use of a hand auger became beneficial, as it was much
more cost effective compared to the hire of a TLB. Masoud et al. (2013) indicates the
cost effectiveness of using a hand auger for investigations. At the shallow excavation
depths encountered, the speed of excitability and in turn data point collection further
supported the beneficial use of a hand auger, especially for the large research supersites.
A total of 21 soil profiles were described in the Nhlowa site and 36 profiles in the
Mooiplaas site. Due to the limited amount of soil excavated with a hand auger as well as
soil weight restrictions that are allowed to be taken out of the KNP only sample sizes for
foundation indicator, X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF) tests
were retrieved from representative selected horizons.
The smaller site investigations provided the opportunity of utilizing a TLB for
excavation of deeper basalt profiles to be inspected, not limited by pristine conditions
such as in the KNP or sample weight limits. This provided the opportunity of sampling
large amounts of soil for compaction testing as well as samples for foundation indicator,
XRF and XRD analysis. Eight test pits where excavated at the Siloam site spaced
approximately 80m to 120m apart. The Roedtan site was investigated with the excavation
of seven test pits across the site also spaced approximately 80m to 120m apart. No XRF
and XRD analyses were done at Roedton, as the investigation occurred before the
commencement of this study. At the Codrington site, only one open profile from a quarry
wall was profiled and sampled in each horizon for foundation indicator, XRF and XRD
analysis, to provide some extrapolative data for Roedtan not having XRD and XRF
information.
The soil profiles were recorded using the standard procedures as per the
guidelines from AEG/SAIEG/SAICE (2002). The use of a hand auger in the KNP
supersites precluded the description of certain attributes of the soil profiles, such as soil
consistency and soil structure. These characteristics if described were based on
experience and professional opinion. For example, with consistency the interpretation
was based on the difficulty of augering as well as the strength and hardness of soil lumps
that were excavated. These intact soil lumps also provided some visual assessment on
the soil structure, be it open structure or slickensided etc.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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The presence of joints and fractures in the weathered basalt excavated by the
auger were determined also by ease or difficulty of augering and size and shape of
weathered basalt gravel retrieved from the auger hole.
4.3 Tests conducted
Disturbed soil samples were selectively retrieved for mineralogical and
geochemical analyses (X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF)) as
well as soil mechanical (foundation indicator, Mod. AASHTO and CBR tests). XRD
analyses were assessed in order to determine both the primary and secondary/alteration
mineralogy of the parent basaltic rock and the weathered residual soil horizons. The XRF
analyses were conducted to assess the element transfer, gain or loss, which occurs with
the weathering process from rock to residual material. Together the XRD and XRF data
were used to determine the mineralogical and chemical compositions of the different soil
horizons, as well as the degree of weathering the soil and rock has undergone.
The foundation indicator tests were conducted in order to determine the
percentage particle size distribution and provide the Atterberg limits of the soil. The
additional Mod. AASHTO (Modified American Association of State Highway and
Transportation Officials) and CBR (California Bearing Ratio) tests that were conducted
at Roetan and Siloam (only available at these sites), provided additional insight in the
compaction characteristics of the residual and highly weathered basalt material. The CBR
value is a relative strength measurement for the subgrade soil or base/subbase aggregate.
The Mod. AASHTO is a standard test procedure used in acquiring the CBR value
and additional information. This includes the maximum dry density and optimum
moisture content of the soil under different compaction efforts. This is determined by
establishing the moisture-density relationship of the material when prepared and
compacted at different Mod. AASHTO compaction efforts and at different moisture
contents (Brink, 1983). The CBR values are also determined, these values are used to
evaluate the mechanical strength of the material for different road layer construction.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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5. RESULTS AND ANALYSIS
This chapter contain the results of the tests conducted on the five different low
relief basalt sites. The chapter will start with an overview of the different profile types
encountered at each site. The focus will be on the profile description, depth and thickness
of horizons, presence of pedogenic material and the sieve analysis for horizons tested.
The chapter will continue onto the chemical and mineralogical results for the parent rock
and soil samples from the XRF and XRD testing for each site. The chapter will end with
the presentation of engineering data on sites that have been tested. This chapter will be a
combination of presented results as well as immediate analysis and comparison where
possible. This was done due to the large size of data and quantity of sites in the study.
This approach was taken so that a coherent flow to the results, discussions and
comparisons between sites can be viewed together to make more sense and create a better
picture of the data. Chapter 6 will summarize important aspects of the discussions.
5.1 Profiles
The emphasis during the soil profile description was placed on the vertical
succession of the different soil horizons. The rather flat-lying nature of the sites creates
very similar profiles with only subtle differences. The separation between the various
vertical soil horizons are based on differences in colour, soil texture, presence and extent
of rock formation and/or pedogenesis in the soil horizons. Descriptions in brackets [ ]
indicate occasional occurrence of the component in the horizon or the horizon itself, as
well as interpreted parameters not easily determined during hand augering, the latter for
the KNP supersites.
It is important to note that minimum thickness does not always represent the
thinnest horizon encountered as certain auger holes/test pits were terminated in a horizon
due to auger refusal and/or inability to extract material. This is also true for maximum
values that does not represent the complete maximum especially for termination of
excavation in a horizon, termination occurred mostly due to the extent of auger/TLB,
refusal of auger and inability to extract material from auger hole.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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5.1.1 Nhlowa Profiles ― Lebombo Basalt
SBProfile 1: Colluvium - residual basalt - highly weathered basalt
Seven similar profiles with the sequence of colluvium, residual basalt then highly
weathered basalt were encountered and described, represented by profiles SB02, SB03,
SB10, SB16, SB17, SB22 and SB23. Summarised below in Table 3.
Table 3: Profile description summary for SBProfile 1 - Nhlowa site.
Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional
Information
Colluvium
• Slightly moist,
• Dark brown,
• [Shattered],
• Slightly gravelly silty SAND /
clayey sand [sandy clay].
0.06{0.28}0.60
*0.19
0.06{0.27}0.60
*0.19
n=7
No pedogenic material
encountered.
Residual
basalt
• Slightly moist,
• Light brown to yellow brown
[medium and red brown],
• [Shattered],
• Silty sand/clayey sand [sandy
clay/silt].
0.53{0.72}1.05
*0.20
0.27{0.43}0.50
*0.06
n=6
Ferricrete nodules as
gravel present, can then
be described as sandy
gravel as well.
SB17 contained
calcrete, the only auger
hole to contain
calcrete.
Highly
weathered
basalt
• Slightly moist,
• Yellow brown,
• Gravelly [silty/clayey] sand.
0.40{0.80}1.25
*0.376
0.04{0.29}0.60
*0.23 n=4
[Ferruginization
present].
[Moderately
weathered
basalt]
• Slightly moist,
• Brown mottled red,
• Silty sandy highly to
moderately weathered basalt
GRAVEL.
SB22 = 0.73
SB23 = 0.40
SB22 = 0.20
SB23 = 0.28
n=2
Only SB22
encountered this layer
with SB23
encountering traces of
the layer in a riverbank.
Min{Average}Max;
* - Standard deviation,
[] - Occasional occurrence;
n - number of data points
Certain profiles such as SB23 consists of a colluvial horizon followed by a highly
weathered basalt layer without a residual layer. Some profiles terminated in the residual
basalt horizon, assumed to be on highly weathered basalt. This occurred at depths where
the highly weathered layer was most likely to occur, based on other profiles. Figure 19
indicate that all horizons of SBProfile 1 consist mostly of silt and sand (silt over all being
dominant) with less amounts of gravel. The highly weathered basalt layer contains much
less silt than the residual layers, where it contains more gravel and sand.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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This is also the case with the residual layer of SB17 which refused on calcrete
nodules containing much more gravel than sand and silt, (SB17 is the only auger hole
that contained calcrete). The colluvial layer has the highest clay content at 17% which
significantly becomes less towards the highly weathered layer with 4.5% clay.
The reverse of this occurs with the gravel content increasing from the colluvial
layer to the highly weathered basalt layer, as indicated in Figure 20. From Figure 20 it
can be seen that the sand content is approximately equal across the three horizons.
Figure 19: Laboratory soil textures for individual horizons for SBProfile 1. Col=Colluvium; Res B=Residual Basalt; HW B=Highly Weathered Basalt
17
7
1812 14 15
4 5
36
25
43
4533 27
19 16
42
40
3741
44
20 57
40
5
27
1 29
37
20
40
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Col (SB02) Res B (SB02) Res B (SB03) Res B (SB16) Res B (SB17) Res B (SB17) HW B (SB03) HW B (SB16)
% Gravel
% Sand
% Silt
% Clay
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Figure 20: Average soil textures for different horizon for SBProfile 1. Col=Colluvium; Res B=Residual Basalt; HW B=Highly Weathered Basalt
SBProfile 2: Reworked residual basalt - [Residual basalt] -
Highly/Moderately weathered basalt.
Eight similar profiles with the sequence starting with a reworked residual basalt
layer and continuing on to one or more of the following layers; residual basalt, highly
weathered basalt and/or moderately weathered basalt were encountered and described.
This sequence is represented by profiles SB11, SB12, SB15, SB18, SB19, SB20, SB21
and SB25. Summarised below in Table 4.
Table 4:Profile description summary for SBProfile 2 - Nhlowa site.
Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional
Information
Reworked
residual
basalt
• Slightly moist,
• Dark brown,
• Open root channels,
• Gravelly silty SAND.
0.13{0.24}0.32
*0.06
0.13{0.24}0.32
*0.06
n=8
No pedogenic
material.
1736
42
5
13.2
34.6
36.4
15.2
4.517.5
48.5
30
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
% Clay % Silt % Sand % Gravel
HiW B Ave
Res B Ave
Col
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional
Information
[Residual
basalt]
• Slightly moist,
• Light brown to reddish brown,
• Silty SAND with Ferricrete
nodules as gravel.
0.60{0.61}0.61
*0.001
0.60{0.61}0.61
*0.001
n=2
Ferricrete nodules
present only as
gravel.
Highly
weathered
basalt
• Slightly moist,
• Light to yellow brown,
• [Jointed],
• Silty SAND with abundant
highly weathered basalt gravel
when excavated OR silty sandy
GRAVEL.
0.15{0.43}0.80
*0.237
0.02{0.20}0.45*
0.16
n=5
No pedogenic
material.
[Moderately
weathered
basalt]
• Slightly moist,
• Light brown mottled orange and
yellow,
• Jointed,
• Sandy coarse GRAVEL of 2cm
to 4cm large basalt fragments.
0.30{0.34}0.38
*0.056
0.06{0.065}0.07
*0.01
n=2
No pedogenic
material.
Min{Average}Max;
* - Standard deviation,
[] - Occasional occurrence;
n - number of data points
The residual basalt horizon occurred in auger hole SB11 which continued to the
highly weathered basalt layer, where SB15 terminated in the residual basalt layer. Only
in auger hole SB11 did the horizon sequence follow the sequence for SBProfile 2,
although the residual basalt layer not being the deterministic feature of the layer. The last
three horizons (residual to moderately weathered basalt) occurred sporadic in the
sequence with the highly weathered basalt horizon present 5 times. The trend of the
horizons either terminates in the residual basalt layer or goes from the reworked layer
over to the highly weathered or moderately weathered basalt layer not encountering the
residual basalt layer. It is important to note that no transported horizon was encountered.
A complete sequence example is presented in Photograph 1.
No laboratory results are available for the material from this profile sequence.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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Photograph 1: SB11 example of SBProfile 2.
SBProfile 3: Residual basalt - Highly weathered basalt.
Four similar profiles with the sequence starting with a residual basalt layer and
continuing on to highly weathered basalt were described and encountered. Represented
by profiles SB26 to SB29. Summarised below in Table 5.
Reworked residual basalt
Residual basalt
Highly weathered basalt
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Table 5: Profile description summary for SBProfile 3 - Nhlowa site.
Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional
Information
Residual
basalt
• Dry to slightly moist,
• Dark brown to black,
• [Open root channels],
• Clayey silty SAND to silty clayey
SAND/sandy CLAY with scattered
gravel as Ferricrete nodules and
scattered highly weathered basalt
possibly from the layer below.
0.33{0.57}0.81
*0.21
0.33{0.57}0.81
*0.21
n=4
Ferricrete nodules
are present in each
residual layer.
Highly
weathered
basalt
• Slightly moist,
• Yellow brown mottled black,
• Gravelly SAND to sandy
GRAVEL of highly weathered
basalt fragments.
0.54{0.81}1.30
*0.35
0.08{0.24}0.49
*0.17
n=4
Ferricrete staining
visible on
fragments.
Min{Average}Max;
* - Standard deviation,
[] - Occasional occurrence;
n - number of data points
The major defining factor in SBProfile 3 was that no cover soil such as colluvium
or a reworked horizon was encountered. This could be the most disturbed portions of the
site in that the top transported horizon present in SBProfile 1 and reworked horizon in
SBProfile 2 has been removed. Only one sample for the residual basalt in auger hole
SB29 was available at a depth of 0.81m to 1.30m the results were as follows:
• Clay – 3
• Silt – 19 %
• Sand – 56%
• Gravel – 20%
• PI – 19%
SBProfile 4: Alluvium
Three profiles were encountered and described in a stream or river, represented
by profiles SB07, SB13 and SB14. Summarised below in Table 6.
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Table 6: Profile description summary for SBProfile 4 - Nhlowa site.
Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness (m)
Additional
Information
Alluvium
• Slightly moist,
• Light to dark greyish brown,
• Stiff,
• (Sandy clay/sandy gravel) to
gravelly SAND.
0.10{0.51}0.94
*0.42
0.10{0.51}0.94
*0.42
n=3
No pedogenic
material.
Min{Average}Max;
* - Standard deviation,
[] - Occasional occurrence;
n - number of data points
Profiles SB07 and SB13 refused due to coarse gravel in the profile, SB13 refused
close to surface. One foundation indicator sample was taken at SB07 0.11m to 0.81m and
provided the following soil texture information: Clay 16%, Silt 18%, Sand 38% and
Gravel 27%.
5.1.2 Mooiplaas Profiles ― Lebombo Basalt Profiles
NBProfile 1: Colluvium - residual soil.
Five similar profiles with the sequence that starts with a colluvium horizon and
progresses to one or more of the following horizons; pebble marker; residual soil and/or
highly weathered basalt were encountered and described. The sequence represented by
profiles NB01 to NB04 and NB26. Summarised below in Table 7.
Table 7: Profile description summary for NBProfile 1 - Mooiplaas site.
Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional
Information
Colluvium
• Slightly moist to moist,
• Medium brown to black,
• [Clayey silty SAND/sandy silt];
[clayey SILT]; [clayey SAND].
0.25{0.33}0.43
*0.08
0.25{0.33}0.43
*0.08
n=5
Variety of soil texture
due to multiple
geological origins.
[Pebble
marker]
• Slightly moist,
• Brown,
• Silty SAND with abundant sub-
angular and rounded quartz gravel.
SB02=0.39 m
SB26=0.47 m
0.04{0.09}0.14
*0.07
n=2
Present in two of the
total 5 profiles (NB02
and NB26).
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Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional
Information
Residual
soil
• Slightly moist,
• [Greyish] Brown [mottled
orange],
• Silty SAND with [calcrete
nodules].
0.50{0.50}0.51
*0.006
0.10{0.17}0.26
*0.08
n=3
The residual
geological origins
encountered here are
gabbro and gneiss.
[Highly
weathered
rock]
• Slightly moist,
• Maroonish brown,
• Silty fine coarse SAND, highly
weathered basalt/gabbro gravel.
0.80m
0.30m
Only NB01 continued
to a highly weathered
horizon possibly
being basalt or
gabbro.
Min{Average}Max;
* - Standard deviation,
[] - Occasional occurrence;
n - number of data points
This profile sequence is variable and limited in that it consists of different
geological origins such as gabbro, rhyolite, sandstone and basalt. This conglomerate of
rock types together occurs at the North West corner of the site. The colluvial layer here,
originates from the mixture of different weathering rates of all the different rock types
juxtaposed together.
It is important to note that the profile sequences following do not contain a
colluvial layer which represents the majority of the basalt site. No samples were retrieved
for this profile type.
NBProfile 2
Profile sequence 2 is split into two sub divisions and not each into their own
profile sequence. The starting/first horizons are close to identical and differ only in the
continuation of the profile sequence into other horizons or early termination of the profile
in a horizon. The early termination a result of hand auger refusal.
27 similar profiles were encountered and described with the sequence starting at
a reworked residual basalt horizon that progresses to one or more of the following layers;
residual basalt; highly weathered basalt and/or moderately weathered basalt.
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NBProfile 2A: Reworked residual - residual basalt.
This sequence is represented by 20 of the 27 profiles by NB05, NB07 to NB11,
NB13, NB14, NB16 to NB25, NB29 and NB33. An excavated example of NBProfile 2A
is in Photograph 2 below and the profile summarised below in Table 8.
Table 8: Profile description summary for NBProfile 2A - Mooiplaas site.
Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional
Information
Reworked
residuum
• Slightly moist,
• Black to dark brown,
• Sandy SILT/silty SAND to
[clayey silt], scattered to minor
calcrete nodules and concretions.
0.21{0.37}0.61
*0.115
0.21{0.37}0.61
*0.115
n=20
6 of the 20 profiles
contained calcrete in
this horizon.
Residual
basalt
• Slightly moist,
• Greyish brown/light brown
mottled white,
• Silty SAND [sandy SILT] with
abundant calcrete nodules and
concretions, calcified horizon.
0.29{0.68}1.07
*0.21
0.07{0.32}0.63
*0.16 n=20
All 20 profiles
contained calcrete in
this horizon.
Min{Average}Max;
* - Standard deviation,
[] - Occasional occurrence;
n - number of data points
The reworked residual basalt horizon contains <10% gravel with the exception of
NB05 containing 18% gravel. The majority of this horizon contains silty sand to sandy
silt material, overall sand being in the majority. The underlying residual basalt layer
contain higher amounts of gravel, 15% to 54%, which in this case is attributed to the
calcrete nodules and concretions on which the hand auger refused, and the profile
terminated. The soil textures are displayed in Figure 21. The residual basalt layer
contains more sand than silt in all four auger holes sampled. Two of the auger holes from
the reworked residual basalt horizon (NB05 and NB11) has higher sand and silt than their
underlying residual basalt layer. The other two auger holes (NB19 and NB20) has less
sand in the reworked residual layer than in the residual layer (although still a higher silt
content), this creates a 50% split between sand and silt dominance with sand slightly in
the majority.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
60
Figure 21: Laboratory soil textures for individual horizons for NBProfile 2A.
The reworked residual basalt contains more silt as well as clay than the residual
basalt layer with averages of 38.8% and 12.2% respectively as opposed to the residual
basalt averages of 19.25% and 6%. Figure 22 below shows that the percentage clay and
silt are higher in the reworked residual basalt than the residual basalt layer which has
undergone less weathering. This could also be attributed to the high presence of calcrete
in the residual basalt layer, by limiting increased weathering activity through cementation
compared to the reworked residual basalt layer.
Photograph 2: NB29 example of NBProfile 2A.
9 12 169
158
39
4
27
39
50
34
44
14
9
2529
46
45
30
49
36
39
34
47 53
18
4 4 8 4
40
54
19 15
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
NB05 NB11 NB19 NB20 NB29 NB05 NB11 NB19 NB20
Reworked residual Basalt Residual Basalt
% Gravel
% Sand
% Silt
% Clay
Reworked Residual Basalt Calcified Residual Basalt
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
61
Figure 22: Average soil textures for different horizons for NBProfile 2A. RewRes B=Reworked Residual Basalt; Res B=Residual Basalt
NBProfile 2B: Reworked residual - Residual basalt - Highly weathered
basalt.
This sequence is represented by 7 of the 27 profiles viz. NB06, NB12, NB15,
NB27A&B, NB28 and NB34. Profile summarised below in Table 9.
Table 9: Profile description summary for NBProfile 2B - Mooiplaas site.
Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional Information
Reworked
residuum
• Slightly moist,
• Black to dark brown,
• Sandy SILT / [silty
SAND] to [clayey silt],
scattered calcrete nodules
and concretions.
0.15{0.35}0.60
*0.18
0.15{0.35}0.60
*0.18
n=6
Only 1 of the 6 profiles
contained calcrete in this
horizon.
Residual
Basalt
• Slightly moist,
• Greyish brown/light
brown mottled white,
• Silty SAND [sandy
SILT] with scattered to
abundant calcrete nodules
and concretions, calcified
horizon.
0.35{0.78}1.48
*0.42
0.20{0.50}1.17
*0.41
n=6
6 of the total 7 profiles
contained calcrete. The one
profile did not encounter the
residual layer.
12.2 38.8
41.2
7.6
6 19.25
43.25
32
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
% Clay % Silt % Sand % Gravel
Ave RewRes B Ave Res B
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Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional Information
Highly
weathered
basalt
• Slightly moist,
• Light greyish brown
[dark grey],
• Clayey silty fine to
coarse SAND GRAVEL
[gravelly sand], gravel of
highly weathered basalt
when augered.
0.45{1.86}3.0
*1.13
0.05{1.47}2.65
*1.12 n=7
Calcrete nodules in 2 of the 7
profiles and calcrete veins
encountered in NB27 and
NB28 profiled in a quarry.
[Moderately
weathered
basalt]
• Dark grey,
• Jointed and fractured,
• Medium hard rock,
calcrete veins encountered
as streaks and patches in
NB27 and NB28.
3 m 2.16{2.49}2.65
*0.28 n=3
NB27A, NB27B and NB28
were profiled in a quarry
from and open face.
(NB27A shown in
Photograph 3)
Min{Average}Max;
* - Standard deviation,
[] - Occasional occurrence;
n - number of data points
NBProfile 2A terminated in the residual basalt layer, presumably refused on
abundant calcrete nodules and concretions or highly weathered basalt. Therefore, the
sequence did not continue on to the highly weathered basalt horizon. NBProfile 2B
contained mostly scattered to moderately abundant nodules and limited concretions
making it possible to auger through to the highly weathered basalt horizon.
Figure 23 displays the soil textures of NBProfile 2B, it portrays similar trends as
Figure 21 for NBProfile 2A in that the gravel content increases from the reworked
residual basalt to the residual basalt which represents the increase in calcrete nodule
formation. The gravel averages for the reworked residual and residual basalts are 18.25%
and 39% respectively. The clay and silt content for the reworked residual basalt of
NBProfile 2B such as for NBProfile 2A is still much higher than the residual basalt, with
the clay and silt content for the reworked residual horizon at 10.25% and 32.75%
respectively compared to the residual basalt horizon at 3.75% and 17.25% respectively.
NBProfile 2A contains a higher content of fines collectively through the profile
as well as individually per horizon, than NBProfile 2B as portrayed by Figure 24.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
63
The total average percentage fines (silt and clay) for the reworked residual layer
for NBProfile 2A is 51% and the residual basalt 25.25%. The reworked residual layer of
NBProfile 2B contains 43% fines and the residual basalt layer 21%.
Photograph 3: Highly to moderately weathered medium hard rock Basalt with calcrete
streaks (Profile in Quarry).
Figure 23: Laboratory soil textures for individual horizons for NBProfile 2B.
13 12 9 7 61 3 5
43
31 35
22 23
209
17
31 55
40
2837
63
33
28
12
2
16
4334
16
5650
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
NB06 NB33 NB34 NB34 NB06 NB12 NB27 NB34
Reworked residual Basalt Residual Basalt
% Gravel
% Sand
% Silt
% Clay
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
64
Figure 24: Average clay and silt content for NBProfile 2A vs NBProfile 2B. RewRes B=Reworked Residual Basalt; Res B=Residual Basalt
NBProfile 3: Alluvium
Three profiles were encountered and described in a stream or river. The alluvial
horizon was underlain by either the reworked residual basalt or residual basalt layer
represented by profiles NB30 to NB32. Profile summarised below in Table 10.
Table 10: Profile description summary for NBProfile 3 - Mooiplaas site.
Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional
Information
Alluvium
• Slightly moist,
• Brown to dark grey to black,
• Silty sand to clayey SILT, and
gravel.
0.24{0.58}0.90
*0.33
0.24{0.58}0.90
*0.33
n=3
Gravel is of mixed
origin and calcrete
nodules on surface but
not in the horizon.
Reworked
residual
Basalt
• Grey streaked and mottled
orange and mottled white,
• Sandy SILT, scattered calcrete
nodules.
Horizon
occurred at
0.90 - 1.20
0.30
Horizon only
encountered in profile
NB31.
Residual
basalt
• Grey brown mottled and
streaked orange brown,
• Sandy SILT, scattered calcrete
nodules.
0.64{0.80}0.72
*0.11
0.03{0.3}0.56
*0.37
n=2
Horizon encountered in
profiles NB30 and
NB32.
Min{Average}Max;
* - Standard deviation,
[] - Occasional occurrence;
n - number of data points
12.2
6
10.25
3.75
38.8
19.25
32.75
17.25
0
5
10
15
20
25
30
35
40
45
Ave RewRes B NB2A Ave Res B NB2A Ave RewRes B NB2B Ave Res B NB2B
Fines in ProfileNB2A vs NB2B
% Clay
% Silt
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
65
Profile NB30 was profiled at a first order stream and NB31 in a second order
stream. NB30 refused on calcrete concretions from a possible reworked residual basalt
horizon where NB32 also refused on calcrete nodules in the residual basalt horizon. Two
sieve analysis tests were done on auger hole NB32 at 0.00m to 0.24m for the alluvial
layer and at 0.24m to 0.80m for the underlying calcified residual basalt. The results
provided the following soil texture information for the alluvial layer: Clay 20%, Silt 25%,
Sand 42% and Gravel 13%; and for the calcified residual basalt layer: Clay 29%, Silt
20%, Sand 37% and Gravel 15%.
5.1.3 Siloam ― Sibasa Basalt Profiles
The profiles at Siloam represents the Sibasa basalts through eight profiles (TP01-
TP08) excavated by a LuiGong 777 TLB to a depth of between 1.50m and 3.20m. Only
one profile sequence with some differences in the horizons are described and summarised
below in Table 11.
Table 11: Profile description summary for Sibasa basalts - Siloam site.
Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional
Information
Colluvium
• Slightly moist to moist,
• Dark brown/brown,
• Stiff [soft, very stiff],
• Open structured and slightly
slickensided,
• Sandy clayey SILT / [sandy silt] to
[silty CLAY], minor to abundant
gravel.
0.65{1.04}1.90
*0.41
0.65{1.04}1.90
*0.41
n=8
No pedogenic
material
encountered.
Reworked
pebble
marker /
residuum
• Slightly moist,
• Red/maroon brown mottled
black/white/red,
• Dense to [very dense, stiff],
• Open structured,
• Silty sandy GRAVEL/sandy
gravelly SILT [clayey silt with
abundant gravel] with abundant sub-
angular cobbles.
1.45{1.76}2.35
*0.35
0.45{0.58}0.75
*0.14
n=5
Ferricrete nodules
encountered in
TP01, TP02 and
TP04.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
66
Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional
Information
Residual
basalt
• Slightly moist,
• Yellow brown mottled/patched
black,
• Dense to very dense,
• [Slightly] pinholed structured,
• Silty/sandy GRAVEL to sandy
gravelly SILT [clayey silt with
abundant gravel] with abundant
rounded to sub-rounded basalt
cobbles, [Scattered Ferricrete
nodules].
1.45{1.76}2.35
*0.58
0.15{1.01}1.85
*0.62
n=8
Ferricrete
encountered in
TP01, TP02 and
TP04.
TP08 contains
patches of highly
to completely
weathered basalt.
[Completely
weathered
basalt]
• Wet,
• Light brown,
• Firm to medium dense,
• Relic rock structure,
• Sandy clayey SILT, scattered highly
to completely weathered basalt
gravel.
Horizon
occurred at
2.50-3.00m
0.50m
No pedogenic
material
encountered.
Min{Average}Max;
* - Standard deviation,
[] - Occasional occurrence;
n - number of data points
The investigated site is too small with no distinct large differences to distinguish
more than one profile type. The typical sequence encountered during excavation was
colluvium underlain by a reworked pebble marker and residuum, residual basalt and one
profile continued into completely weathered basalt. Photograph 4 displays a basic soil
profile on site.
The colluvial horizon contained the highest amount of clay with an average
(standard deviation) of 26.50% (15.02%) followed by the residual layer with 14.83%
(9.26%). The highest percentage of fines are also present in the colluvial layer with an
average of 50.75% followed by the residual layer at 35.49%. The high fines content most
likely attributed to the site being located close to the footlope of the mountain. The
reworked pebble marker as expected, contained the highest gravel content at an average
of 51%.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
67
Photograph 4: Typical Sibasa Basalt profile example, TP01.
5.1.4 Roedtan ― Springbok Flats Basalt Profiles
The profiles at Roedtan represents the Springbok Flats basalt excavated by a JCB
3CX TLB down to a depth of between 2.10m to 2.50m with an average depth of 2.30m.
Only one profile sequence with some differences in the horizons are described as the
profiles encountered were constant across the site. Summarised below in Table 12.
Table 12: Profile description summary for Springbok Flats basalts - Roedtan site.
Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional
Information
Colluvium
• Slightly moist to moist,
• Maroon/red brown,
• Medium dense to dense,
• Pinholed structured,
• Clayey silty SAND.
0.26{0.33}0.40
*0.05
0.26{0.33}0.40
*0.05
n=8
No pedogenic
material
encountered.
Colluvium
Reworked Pebble Marker
MMM???marker/Residuum
Residual Basalt
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
68
Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional
Information
Calcified
residual
basalt
• Slightly moist,
• Red/orange brown mottled/patched
white,
• Medium dense to dense,
• Open [pinholed] structured,
• Silty gravelly SAND/silty sandy
GRAVEL with gravel of weathered
basalt and calcrete concretions and
nodules.
0.55{0.83}1.20
*0.24
0.29{0.50}0.85
*0.21
n=8
Calcrete
encountered in
TP02 to TP07.
Patches of
horizontally
layered and
fractured
completely/highly
weathered basalt,
Completely
to Highly
weathered
Basalt
• Slightly moist,
• Streaked orange brown and black
mottled white,
• Dense to soft rock,
• Fractured and horizontally layered,
• Silty sandy GRAVEL with gravel
of weathered basalt, [patches of
moderately weathered basalt],
[patches of calcification.]
1.10{1.75}2.50
*0.47
0.50{0.92}1.80
*0.45
N=5
Calcrete nodules
encountered in
TP01.
[Highly to
Moderately
weathered
Basalt]
• Slightly moist,
• Streaked black and orange,
• Highly fractured and horizontally
layered,
• Soft rock to medium hard rock,
• Excavates to sandy GRAVEL with
gravel of moderately weathered
basalt.
2.40{2.43}2.50
*0.06
0.60{0.83}1.30
*0.40
n=3
Calcrete
encountered only
as scattered
patches.
Min{Average}Max;
* - Standard deviation,
[] - Occasional occurrence;
n - number of data points
The basic profile horizon sequence was colluvium, calcified residual basalt,
completely weathered basalt, highly weathered basalt with patches of moderately
weathered basalt in the latter two horizons. These latter two horizons are described as a
combination such as completely to highly weathered basalt due to mixed portions of both
completely and highly weathered basalt present in the horizon. In some profiles a definite
distinction could be made although due to the undulated weathering in the horizon this
was not the majority of the time. The dominant soil texture in these profiles is gravel and
sand in the residual and weathered basalt horizons. The sand content in the calcified
residual basalt is higher than the completely/highly weathered basalt horizon with an
average (standard deviation) of 36.33% (6.66%) and 27% (4.47%) respectively. The high
gravel content in the calcified residual basalt layer is attributed to the calcrete nodules
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
69
and concretions as well as weathered basalt gravel: Ave. 48% and Stdev. 8.71%.
Although this is still less than the weathered basalt horizons that has a highly fractured
structure and excavates to mostly gravel: Ave. 67.20% and Stdev. 5.58%. The fines
content is extremely low in both these horizons at <5% present.
Photograph 5: Typical Springbok Flats Basalt profile example, TP02.
5.1.5 Codrington ― Springbok Basalt Profiles
Only one profile was described in an open quarry as a reference point to the
Springbok Flats basalt in the Roedtan site. Profule summarised below in Table 13, and
typical profile depicted in Photograph 6.
Colluvium
Calcified residual basalt
Completely /
Highly weathered
basalt
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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Table 13: Profile description summary for Springbok Flats basalts - Codrington site.
Horizon Horizon Description
Base of
horizon below
ground level
(m)
Horizon
Thickness
(m)
Additional
Information
Residual
basalt
• Dry,
• Dark brown mottled white,
• Loose to soft,
• Shattered,
• Silty clayey fine SAND/silty
sandy CLAY (with calcrete nodules
and concretions).
1.00m 1.00m n=1
Calcrete
encountered in top
residual horizon
Highly
weathered
basalt
• Dry,
• Olive brown speckled white &
orange,
• Loose,
• Intact,
• Gravelly silty SAND.
2.00m 1.00m
No calcrete
encountered.
Min{Average}Max;
* - Standard deviation,
[] - Occasional occurrence;
n - number of data points
Photograph 6: Basic profile example at Codrington, S01.
Residual basalt (TOP)
Highly weathered basalt
Residual basalt (BOTTOM)
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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5.2 Chemical and Mineralogical Analysis
As indicated above the basalt from the Nhlowa site is mostly or entirely
underlain by the Sabie River formation, which according to Duncan and Marsh (2006)
are tholeiitic (olivine poor) basalt in composition. The Mooiplaas site is partly or
entirely underlain by the Letaba Formation, picritic (olivine rich) basalt. The basalt
magma series can be divided into two groups viz. alkaline and subalkaline, where the
subalkaline group is further divided into tholeiitic and calc-alkaline basalt. A summary
of the characteristics of tholeiitic basalt from the subalkaline subgroup and alkaline
group can be seen above in Chapter 1 in Figure 1.
The alkaline basalts area characterized by having a lower silica content (silica-
undersaturated) and have higher contents of alkalis such as sodium (Na2O) and potassium
(K2O) than the tholeiitic basalts series. The tholeiitic basalt series contain higher iron
content whereas the calc-alkaline comprises of more magnesium and alkalis (Na2O) than
tholeiitic basalt, as portrayed by the AMF diagram in
Figure 2.
The basalts of the Springbok Flats according to SACS (1980, cited in Marsh
1984) was originally correlated to the Letaba formation of the Lebombo Group. This
name was collectively given to all basalts that were located below the rhyolites in
Lebombo. Although after additional investigations it was found that the Springbok Flats
were chemically and petrographically different to the Letaba Formation basalts.
Additional data presented by Marsh (1984) indicated the Springbok Flats are more
closely associated to the Sabie River Formation and Lesotho Formation, although having
a stronger supporting correlation to the former.
The AMF diagram in Figure 25 indicates where the Nhlowa, Mooiplaas and
Springbok Flats basalts at Codrington plot according to the XRF data gathered. From the
profile descriptions above it can be observed that the Nhlowa and Mooiplaas sites do not
weather similarly and in turn creates different profiles and soil characteristics. One
notable difference between the two profiles is the formation of different pedocretes viz.,
ferricrete at Nhlowa in the south and calcrete at Mooiplaas in the north.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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This can be accredited to differences in parent rock mineralogy as well as
different climates conditions (such as rainfall and/or evaporation), this contributes to
different soil forming processes as a generalization on Weinert’s N value (Brink, 1979).
Figure 25: The Karoo basalts plotted on the AMF diagram for Tholeiitic and calc-
alkaline basalt determination (adapted from Winter, 2001).
Smith et al. (2013) indicate that the northern Mooiplaas site receives less annual
rainfall than the southern Nhlowa site. The average rainfall for the Mooiplaas site is
480mm/annum (to the closest 10mm/annum) and the Nhlowa site 610mm/annum.
Rainfall records between 1940-1941 and 2010-2011 from stations near the sites were
used in calculating the average rainfall.
The Siloam site has similar rainfall as the Nhlowa site and the Springbok Flats
Basalts of Roedtan and Codrington have similar lower rainfall to the Mooiplaas site. The
Siloam, Roedtan and Codrington sites also differ in that the soil profiles at the Siloam
site contain ferricrete whereas those at the Roedtan and Codrington sites contain calcrete
similarly to the Nhlowa and Mooiplaas site respectively.
Springbok Flats at Codrington
Nhlowa site
Mooiplaas site
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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5.2.1 XRF Analysis — Rock
5.2.1.1 Mooiplaas and Nhlowa
The Mooiplaas rock analyses had six rock samples available in contrast to
Nhlowa with only two samples, for the latter from a jointed rock mass and one containing
visible amygdales. From a chemical/elemental point of view as displayed by Table 14
and Figure 26 no key differences in the major elements (Fe and Ca) of the sampled parent
rocks from the two sites can be distinguished. Key differences in respect to the Fe and
Ca contents present is in excess and contribution to calcrete formation at the Mooiplaas
site in the northern basalts, and ferricrete formation at the Nhlowa site in the southern
basalts. The Fe and Ca contents between the two sites are very similar. With the Fe
contents of the Mooiplaas and Nhlowa site at 12.29% and 12.43% and the Ca contents at
8.81% and 7.71% respectively.
The abovementioned indicates the amount of Fe and Ca in the parent rock, is not
in excess in either of the rocks from the sites. From this information the amount of Fe
and Ca in the rock possibly being in excess at one site to the other is not the determining
factor for different pedogenic formation. It is reasonable to believe the distinctive
pedogenic formations between the two sites are possibly not determined by excess of one
element to the other. The differences in type of mineralogy and weathering properties in
different climatic environments all contribute to different pedogenic formations. The type
and intensity of weathering these different mineral assemblages undergo determines
which elements get transported or precipitated.
Notable differences in the elemental concentrations between the Mooiplaas and
Nhlowa basalt rock is evident for Al and Mg. The average Al concentrations are higher
in the Nhlowa basalt rock at 14.60% than the Mooiplaas basalt rock at 10.86%, where
the reverse occurs with the average Mg concentrations of 5.22% in the Nhlowa basalt
rocks and 8.38% for the Mooiplaas basalt rocks. The alkali content of the parent rocks
between the two sites are very similar when considering the averages. When
considering the standard deviation at the Mooiplaas site for the Na2O content, the
Mooiplaas site contains rock samples with higher sodium contents.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
74
Table 14: Average rock element concentrations for the Mooiplaas and Nhlowa
sites.
Rock samples
Mooiplaas Nhlowa
XRF
(wt%) Average
Standard
Deviation
Average
Standard
Deviation
SiO2 46.64 4.40 50.89 1.27
TiO2 2.95 0.54 2.21 1.53
Al2O3 10.86 1.59 14.60 0.03
CaO 8.81 1.21 7.71 1.12
Fe2O3 12.29 0.73 12.43 0.04
MnO 0.18 0.03 0.16 0.05
MgO 8.38 3.76 5.22 1.88
Na2O 3.81 2.67 3.32 0.28
K2O 1.56 0.77 2.16 1.15
P2O5 0.54 0.28 0.40 0.37
Cr2O3 0.06 0.06 0.02 0.01
NiO 0.04 0.03 0.00 0.00
V2O5 0.06 0.00 0.05 0.003
ZrO2 0.03 0.02 0.03 0.03
CuO 0.02 0.01 0.00 0.00
LOI 3.25 2.85 2.36 0.56
TOTAL 99.49 0.25 101.56 0.42
Y (ppm) 29.17 8.76 36.07 14.15
Zr (ppm) 336.17 117.17 282.23 272.15
Higher value than other site
Lower value than other site
Similar values between sites
The less mobile element Titanium (Ti) for the two sites are very similar with the
Mooiplaas site slight higher, average concentration of 2.93% and Nhlowa of 2.21%. The
lower standard deviation of the Ti of the Mooiplaas site indicates a more constant
concentration in the rock samples and the Nhlowa site with very high or low
concentrations. The trace elements Yttrium (Y) and Zirconium (Zr) for the two sites
somewhat do drastically differ from each other. The Y concentration of the Mooiplaas
site is 29.17ppm which is lower than the Nhlowa site at 36.07ppm. The Mooiplaas site
has more constant concentrations of Y from a minimum of 19ppm to a maximum of
38ppm.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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The same trend for the Mooiplaas site occurs with Zr where the concentrations
are 336.17ppm with very similar concentrations in all the samples with a minimum at
213ppm and maximum at 465ppm. The Zr concentrations for the Nhlowa site are similar
to Ti whereby it has either very high or low values, in the case for Zr 474.66ppm to
89.79ppm.
Figure 26: Major element change between Nhlowa (SB - southern basalts) and
Mooiplaas (NB - northern basalts) sites.
5.2.1.2 Codrington
No fresh or weathered rock samples were tested for the Sibasa basalts at Siloam
as well as for the Springbok Flats basalts at Roedtan. For the Springbok Flats basalt at
Codrington one highly weathered basalt sample was taken from profile at 1.00m to 2.00m
as well as a slightly weathered rock sample. The Ca content for the Codrington site in
both rock samples are higher than the Mooiplaas and Nhlowa sites, the highly weathered
basalt at 10.08% and the slightly weathered basalt at 9.86%, only 1.00% to 2.00% higher.
12.2912.43
10.86
14.60
8.38
5.22
8.81
7.71
3.813.32
1.562.16
0.00
5.00
10.00
15.00
NBSB
Avg
wt%
Sites
Fe
Al
Mg
Ca
Na2O
K2O
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76
The Fe content for the Codrington site samples are less than the KNP sites with
1.00% to 1.50%, the highly weathered basalt at 10.70% and the slightly weathered basalt
at 11.09%.
The Mg and Al contents of the highly and slightly weathered basalt for the
Springbok flats at Codrington are very similar, Mg at 5.84% and 6.21% and Al at 14.33%
and 14.85% respectively. These values are also very similar to the Nhlowa site values of
Mg 5.22% and Al 14.60%. The Mooiplaas site has lower Al contents at 10.86% and
higher Mg contents of 8.38% than the Codrington site representing the Springbok flats
basalt.
The alkali contents of Na2O and K2O are much lower than both of the KNP
supersites especially the K2O content. The K2O content for the highly and slightly
weathered basalt of the Springbok Flats are 0.51% and 0.46% respectively, whereas
Nhlowa is 2.16% and Mooiplaas is 1.56%. The Na2O content for the highly weathered
basalt at the Codrington site is 1.91% and the slightly weathered basalt is 2.12%; this is
1.20% to 1.90% less than at Mooiplaas and Nhlowa. These values together with all other
individual XRF data can be viewed in Appendix B.
The Ti, Y and Zr concentrations of the highly and slightly weathered basalt
samples are very similar to their respective samples. The Ti content of the highly
weathered basalt is 0.93% and slightly weathered basalt is 0.97%, which is much lower
than the KNP supersites.
The trace elements Y for the highly weathered basalt and slightly weathered
basalt are very similar to each other, the same for Zr. The Y for the highly weathered
basalt is 21.00ppm and slightly weathered basalt is 23.00ppm. The Zr content is 107ppm
for the highly weathered basalt and 105ppm for the slightly weathered basalt. The Y
content at Codrington is similar to the averages of the Mooiplaas site but less than the
Nhlowa site. The Zr content at Codrington is generally much less than both the KNP sites
with some samples slightly higher.
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5.2.2 XRD Analysis — Rock
5.2.2.1 Mooiplaas and Nhlowa
Table 15 below indicates the average XRD concentrations for rock samples from
the two KNP supersites. Mineral percentages per rock sample differ at times for example
by 16% from each other (indicated by the standard deviations), this as a result that certain
minerals aren’t always present in the rock. Differences between the mineral
configurations of the KNP supersites are as follows: the pyroxene mineral Augite
[(Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6] is only present in the northern basalt rocks at
Mooiplaas, whereas Diopside (commonly MgCaSi2O6, part of the solid solution series
with Augite) is only found in the southern basalt rocks at Nhlowa.
The Mg endmember of pyroxene, Enstatite (MgSiO3), was also only found in the
southern basalt rocks. Olivine was found to be only present in the northern basalt rocks
in two samples, as Forsterite the Mg endmember. The rock sample at Codrington
representing the Springbok Flats basalts also only contain Augite and no Diopside or
Enstatite, similar to the northern basalt samples although it contains no Forsterite
(olivine).
The northern basalt rocks from the Mooiplaas site differ largely from each other
across the site in mineral content, this is indicated by Table C4, Appendix C depicting
the individual XRD rock sample results. Rock samples from Outcrop 4 and 5 show
similar mineral assemblages and concentrations although differ almost completely from
the other samples. For example. rocks taken at auger hole NB17 and NB29 also indicates
similar mineral assemblages and concentrations to each other. These two rock pairs (from
outcrops and auger holes) at Mooiplaas differ from each other in the following aspects:
• The outcrop samples contain the minerals Magnetite, Hematite and Hornblende
whereas the rocks at NB17 and NB29 do not.
• The outcrop rock samples do not contain any feldspar minerals such as
Plagioclase, Orthoclase or Microcline whereas the rock samples at NB17 and
NB29 contain high concentrations of Plagioclase (29.86% to 37.20%
respectively), although Outcrop 4 contains the feldspathoid mineral Nepheline.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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• The outcrop rock samples do not contain any feldspar minerals, in turn they
contain other tectosilicate minerals such as Analcime (NaAlSi2O6·H2O) (Outcrop
4 at 11.53% and Outcrop 5 at 11.98%) and Natrolite (Na2Al2Si3O10·2H2O)
(Outcrop 4 at 12.25% and Outcrop 5 at 14.40%).
• The Mg endmember of Olivine (Forsterite) is also only present in the rock
samples from NB17 and NB29 (2 out of the 6 samples).
The southern basalt rocks from the Nhlowa site contain minerals such as Chlorite
and already mentioned Enstatite, which are not present in the northern basalt rocks from
the Mooiplaas site. The southern basalt rock samples do not contain the tectosilicate
minerals of Analcime and Natrolite although they do contain Plagioclase and Microcline.
According to Figure 1 a tholeiitic basalt contains no olivine (olivine poor), no
alkali feldspar, Microcline and Orthoclase, but contains Augite. The southern basalt
rocks which should class as a tholeiitic basalt, plots on the border of the tholeiitic and
calc-alkaline boundary. These rocks do in fact not contain Olivine as a tholeiitic basalt
should. Although is also in contrast to a tholeiitic basalt which does not contain Augite
and does contain Microcline an alkali feldspar.
The northern basalt rocks plot in the calc-alkaline section of the AMF diagram in
Figure 25, which is described as Mg rich and higher in alkalis (Na2O+K2O). The northern
basalt rocks which is described as picritic (olivine rich) only contain olivine in 2 of the 6
rock samples, contains Augite in all 6 samples and also contain Orthoclase an alkali
feldspar. The XRF data also indicate that the Mooiplaas site has higher Mg than the
Nhlowa site. Individual XRD data can be viewed in Appendix C.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
79
Table 15: Average mineral concentrations for the Mooiplaas and Nhlowa sites.
Rock samples Mooiplaas Nhlowa
XRD (wt%) Average Standard
Deviation
Average
Standard
Deviation
Augite 42.15 13.61 0.00 0.00
Diopside 0.00 0.00 15.65 22.13
Chlorite 0.00 0.00 20.51 3.25
Muscovite 0.93 1.68 4.07 5.76
Enstatite 0.00 0.00 2.09 2.96
Goethite 0.00 0.00 0.00 0.00
Kaolinite 0.00 0.00 0.00 0.00
Ilmenite 1.26 2.01 0.00 0.00
Magnetite 3.40 3.93 0.00 0.00
Hematite 0.62 0.98 0.71 1.00
Hornblende 1.20 2.95 2.23 3.15
Forsterite 5.57 9.49 0.00 0.00
Microcline 0.00 0.00 15.96 22.57
Orthoclase 1.59 3.89 0.00 0.00
Plagioclase 11.18 17.47 31.22 3.51
Quartz 0.00 0.00 2.16 3.05
Smectite 9.38 22.98 0.00 0.00
Titanite 0.00 0.00 5.42 7.66
Calcite,
magnesian 0.82 2.02
0.00 0.00
Palygorskite 0.00 0.00 0.00 0.00
Anatase 0.00 0.00 0.00 0.00
Analcime 4.48 5.79 0.00 0.00
Actinolite 1.54 3.76 0.00 0.00
Natrolite 12.82 19.49 0.00 0.00
Nepheline 2.32 5.68 0.00 0.00
Laumonite 0.75 1.84 0.00 0.00
Total 100.00 - 100.00 -
Higher value than other site
Lower value than other site
5.2.2.2 Codrington
The highly and slightly weathered basalt from the Springbok Flats samples are
already altered containing 35.85% and 23.96% of a secondary mineral Smectite, whereas
the Mooiplaas site only contained one sample with Smectite of 56.29%. The remaining
five rock samples and the Nhlowa site contain no smectite.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
80
This is a possible indication for why the Springbok Flats have such low Augite
concentrations of 19% to 24% and the average found at the Mooiplaas site is 42.15%.
The rock sample from Codrington only contains Augite with no Diopside or Enstatite,
similar to the northern basalt samples although contain no Forsterite (olivine) which the
Mooiplaas site does.
5.2.3 XRF Analysis — Soil
5.2.3.1 Mooiplaas and Nhlowa
Figure 27 and Figure 28 below indicate and focus on different Fe and Ca
concentrations in the profile sequence between the Mooiplaas and Nhlowa supersites at
the KNP. This portrays different processes and conditions of leaching, precipitation and
transportation of Fe and Ca in the profiles and individual horizons between the two sites.
For the Nhlowa site high Fe content is found in the different horizons attributed
to the presence of ferricrete. The Fe content increases from the underlying parent rock
upwards through the profile to the colluvial horizon. A possible mechanism is Fe that
gets leached out of the underlying parent rock and precipitated in and through the profile
by fluctuating shallow seasonal seepage water which leads to ferricrete formation. The
cementation of Fe sesquioxides in the soil to form ferricrete results in a higher
concentration of Fe in the residual and highly weathered basalt layers than Fe content in
the parent rock. With a high Fe concentration in the colluvial layer as well it indicates
that the Fe concentration is possibly also attributed to transported Fe, such as with the
formation of laterite. The Ca content decreases from the underlying parent rock upwards
to the colluvial layer in contrast to the increase in Fe. The average Ca content in the rock
samples is less than the Fe content portrayed in Figure 27.
The Mg concentrations also decrease from the parent rock up through the profile.
This indicates that certain Ca and Mg bearing minerals weather more readily in the high
rainfall area of the Nhlowa site, which results in Ca and Mg mobilizing early in the
eluviation process.
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Figure 27: Major element mobilization in Southern Basalt horizons (Nhlowa).
In contrast to the Nhlowa site, Fe gets leached out and transported at the
Mooiplaas site whereas Ca gets precipitated in the soil profile which leads to calcrete
formation, Figure 28. The calcrete concentration is focused in the residual basalt and
highly weathered basalt layer which is higher than the parent rock’s concentration similar
to the Fe concentration in the Nhlowa site. Calcium concentrations drop below the parent
rock’s level in the reworked residual basalt and colluvial layers where erosion processes
transport the Ca away more readily. This strengthens the likelihood that an increase in
concentrations in the profile is introduced from other sources as well.
From Figure 28, one can see that the Al concentration at the Mooiplaas site
decreases from the parent rock to the residual basalt layer similarly to the Nhlowa site.
From the residual basalt horizon, the Al concentrations increases most likely due to Al
input from transported sources. The Mg concentrations initially increase form the parent
rock to the highly weathered rock, further on the concentrations decrease through the
horizons up to the colluvial layer.
0.00 5.00 10.00 15.00 20.00
Colluvium
Residual Basalt
Highly weathered Basalt
Rock sample
Avg wt%
Laye
rs
ColluviumResidual BasaltHighly weathered BasaltRock sample
Fe 18.3716.2114.1412.43
Al 11.5712.1313.1114.60
Mg 1.092.343.925.22
Ca 0.805.016.727.71
Ti 3.493.062.862.21
Element mobilization in Southern Basalt Horizons
Fe
Al
Mg
Ca
Ti
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82
Figure 28: Major element mobilization in Northern Basalt horizons (Mooiplaas).
A decrease in the Na content occurs in both the Mooiplaas and Nhlowa sites, the
decrease at the Mooiplaas site from parent rock to highly weathered basalt is drastic,
from 3.81% to 0.80% and the drop to the residual layer only slight at 0.60%. The drop at
the Nhlowa site is not as drastic with the parent rock at 3.52% to the highly weathered
basalt at 1.85% and residual basalt at 0.90%. The K content at Nhlowa decreases in a
similar manner as the Na, although at the Mooiplaas site the K content increases above
the parent rocks concentration.
The standard deviations for the Ti content for both sites are mostly around 1.00%
and some >0.50%. The Ti content in both the Mooiplaas and Nhlowa sites behave
similarly to the Fe content. At the Nhlowa site Ti increases from the parent rock to the
colluvial layer similar to Fe. The Ti content similar to the Fe content at the Mooiplaas
site decreases from the parent rock to the residual horizon.
0.00 5.00 10.00 15.00
Colluvium
Alluvium
Reworked Residuum
Residual Basalt
Highly weathered Basalt
Rock sample
Avg wt%
Laye
rs
ColluviumAlluviumReworkedResiduum
Residual BasaltHighly
weatheredBasalt
Rock sample
Fe 9.529.2410.537.949.5712.29
Al 13.277.308.897.057.0810.86
Mg 2.948.375.435.539.248.38
Ca 3.456.165.5811.9813.488.81
Ti 1.442.322.872.082.792.95
Element mobilization in Northern Basalt horizons
Fe
Al
Mg
Ca
Ti
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83
The Ti increases in the reworked residual horizon and decreases again in the
colluvial horizon. The Y and Zr content in both sites show an increase and decrease from
the parent rock upwards through the profile, Table 16. Although some standard
deviations are large at 10ppm to 14ppm for Y and 100ppm to 200ppm for Zr, a
mobilization of these elements are still occurring from the parent rock through the profile.
Table 16: Movement of average trace element concentrations of the sites.
Element Horizon Nhlowa Mooiplaas Codrington Siloam
Y (ppm)
Reworked residual - 30.88 - -
Residual 44.29 24.67 25 29.57
Highly Weathered 50.08 24.60 21 -
Rock 36.07 38.00 *23 -
Zr (ppm)
Reworked residual - 372.63 - -
Residual 340.76 311.47 174 149.86
Highly Weathered 307.80 319.61 107 -
Rock 282.02 465.00 *105 -
* Sample was slightly weathered
5.2.3.2 Codrington and Siloam
The average Fe content in the residual basalt horizon of the Sibasa basalts at
Siloam is 14.45% with a minimum of 12.88% and maximum of 17.18%. In the Springbok
Flats basalt at Codrington, the top residual horizon has 14.80% Fe and the underlying
residual horizon has 9.07% Fe. For the highly weathered basalt at Codrington the Fe
content is 10.70% with the slightly weathered rock at 11.09%.
The Fe content in the residual basalt horizon of the Sibasa basalts at Siloam are
very similar to the southern basalts at Nhlowa, for the average highly weathered basalt
the Fe content is 14.14% and for the average residual basalt it is 16.21%. The highly
weathered basalt at Codrington is closer to the average highly weathered basalt at the
Mooiplaas site of 9.57%.
The Na and K content at Codrington behaves similarly to Mooiplaas where the
Na content decreases and the K content increases although only slightly. Profile TP08 at
Siloam indicates a decrease of Na and K from 3.00m up to 0.70m through the profile
similarly to Nhlowa, see Appendix B.
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The Y and Zr in both the Codrington and Siloam site shows and increase upwards
through the profile. At Codrington the Y first decreases from the slightly weathered basalt
to the highly weather basalt, afterwards it increases again although slightly in the top
residual horizon, Table 16. The Zr content at Codrington increases from 105ppm for the
slightly weathered basalt to 202ppm at the top residual horizon. As for the Siloam site
the average Y content also increases from the residual to colluvial horizon with 29.57ppm
to 34.67ppm. Excluding the colluvial horizon (a transported horizon) and considering the
in-situ material such as the residual basalt an increase is still noticed.
TP08 consists of three different residual horizons sampled at 0.70m to 1.10m,
2.00m to 2.50m and 2.50m to 3.00m, the Y first decreases but ultimately still increases
from the bottom horizon to the top from 27ppm, 23ppm to 32ppm. The same occurs with
the Zr content where it decreases from 119ppm to 115ppm and then increases to 184ppm.
This portrays the mobility of both these elements. In TP05 an increase of both Y and Zr
occurs in the two residual basalt horizons. Yttrium increases from 29ppm at 1.70m to
32ppm at 0.80m and Zirconium increases from 156ppm to 167ppm at these same depths,
individually displayed in Table B7, Appendix B.
The region of Siloam and the Nhlowa site receives similar high rainfall of
approximately 600mm/annum. Compared to the lower rainfall regions such as Mooiplaas
and Springbok Flats at the Codrington site (no XRF was conducted at Roedtan) an
approximate 400mm/annum is received. This attributes to the similar high Fe contents of
the Nhlowa and Siloam site and presence of ferricrete in the profile.
Similarly, with the low average Ca contents in the residual basalt horizon at
Siloam with 6.35% and Nhlowa with 5.01%. Likewise, with the low Fe content of the
Codrington and Mooiplaas site. Although no XRF was taken at Roedtan in order to
compare Ca percentages, through visual inspection it was noticed that both horizons
contained large extents of calcification in the profile. See Tables B1 to B7, Appendix B
for individual data values.
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5.2.4 XRD Analysis — Soil
5.2.4.1 Mooiplaas and Nhlowa
Some contrasting/peculiar information was found from the results between the
rock samples and weathered profile samples for the KNP supersites. Plagioclase and
Quartz are present in relatively high percentages in the residual and highly weathered
basalt horizons at the Mooiplaas site, where little to nothing was present in the rock
samples from the site. Especially Quartz which is not present in any of the 6 rock samples
from the Mooiplaas site, is however present in more than 80% of the reworked residual
basalt, residual basalt and highly weathered basalt horizons, portrayed in Table C2 to
Table C4, Appendix C.
A similar situation occurs at the Nhlowa site where the results from rock sample
SB10A only indicates 4.31% Quartz present in the rock and 0.0% in SB10J, whereas all
the samples from the residual and highly weathered basalt horizons contain high
percentages of Quartz. The highly weathered basalt has 4% to 10% Quartz and the
residual basalt 22% to 66%. Some of the Quartz in the residual basalt could be attributed
to a reworked component between the colluvial and residual layer at both the Nhlowa
and Mooiplaas site. This a high possibility in the reworked residual basalt layer at the
Mooiplaas site.
The parent rock from the Mooiplaas site, based on the XRD results, only contain
the pyroxene mineral Augite, and the rock samples from the Nhlowa site Diopside. The
weathered profile horizons of the Mooiplaas site in contrast to the rock samples contain
more Diopside (present in more samples) than Augite. For example, the residual basalt
layers of the Mooiplaas site contains Diopside in 12 of the 17 samples with minimum
concentrations of 3.86% and maximum of 24.20%. The Augite and Diopside
concentrations in the weathered horizons are notably lower than the Augite
concentrations in the parent rock. This can be attributed to the inherent instability of these
minerals resulting in progressive weathering.
The percentage of the clay mineral Smectite in a sample from a horizon can be
used, to some degree, to determine the extent of weathering which has taken place, or
that weathering has occurred. From the parent rock to the weathered horizons; this would
be the breakdown of original/primary minerals in the parent rock to secondary minerals.
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86
Smectite is present in almost every sample of the weathered horizons from the
Mooiplaas site. The Nhlowa site does not have this high occurrence of the clay mineral,
containing Smectite of 18.22% in only one sample. For the Mooiplaas site the reworked
residual basalt horizon contains the highest smectite content. The residual basalt and
highly weathered basalt contain very similar amounts to each other based on the averages
and standard deviations, which is less than the reworked residual basalt. The minimum
and maximum percentages of smectite for these horizons are as follows (not including
0.00%):
• Reworked residual basalt – 38.83% and 65.92%;
• Residual basalt – 22.05% and 57.47%;
• Highly weathered basalt – 25.85% and 52.43%.
The averages of these horizons are displayed in Table 17 with individual data
sets in Tables C1-C4, Appendix C. The samples from the Nhlowa site lacks other clay
minerals except the phyllosilicate mineral chlorite.
Based on the results, the Smectite clay mineral may originate from the weathering
and break down of Augite, Plagioclase, Magnetite, Hematite, Forsterite and the
tectosilicates Analcime and Natrolite. Given that the Smectite content increases as these
other minerals decrease. This is especially notable at Mooiplaas with the likelihood that
Augite weathers to Smectite. From the parent to highly weathered rock, the Augite
content drastically decreases, while the Smectite content drastically increases, see Table
17. Nhlowa site which does not contain any Augite results in having drastically less to
no Smectite. The tectosilicates mentioned above are only present in the Mooiplaas basalt
parent rock mineral assemblages, and not present in any of the weathered horizons or in
the Nhlowa basalt rocks.
5.2.4.2 Codrington and Siloam
The residual basalt horizon at Siloam contain a range of Quartz contents from
minimum of 3.77% to a maximum of 27.37% similar to the Nhlowa site, although with
not such a large range from minimum to maximum. Whereas the Quartz content at
Codrington has a similar trend as the Mooikloof site where the highly and slightly
weathered basalt at Codrington has low Quartz content of 3.14% and 5.13% respectively
and increases dramatically in the top and bottom residual basalt layer of 34.95% and
20.39% respectively.
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87
The presence of pyroxene in the residual basalt at Siloam is occasional, with one
sample containing Diopside and two with Augite. No Diopside is present in the
Codrington samples although the Augite content decreases from the slightly weathered
basalt of 24.73% to the highly weathered basalt of 19.59%, with the bottom and top
residual basalt of 14.52% and 0.00% respectively. The Plagioclase content also decreases
drastically in the Codrington sample from the slightly weathered basalt to residual basalt.
The Plagioclase in the residual basalt at Siloam has a similar range to its Quartz content
with a minimum Plagioclase of 3.20% and maximum of 26.45%, no rock sample was
tested at Siloam.
Table 17: Mineral summary across horizons for Plagioclase, Diopside, Augite
and Smectite.
Sites Minerals (wt%)
Reworked
Residual
Basalt
Residual
Basalt
Highly
Weathered
Basalt
Parent
Rock
Mooiplaas
Plagioclase 9.18 8.30 17.22 11.18
Diopside 5.63 9.42 10.36 0.00
Augite 5.55 1.97 6.99 42.15
Smectite 41.34 36.7 36.89 9.38
Codrington
Plagioclase - 9.04 41.42 *43.95
Diopside - 0.00 0.00 *0.00
Augite - 7.26 19.59 *24.73
Smectite - 38.78 35.85 *23.96
Nhlowa
Plagioclase - 12.88 38.74 31.22
Diopside - 1.19 17.96 15.65
Augite - 0.00 0.00 0.00
Smectite - 4.56 29.67 0.00
Siloam
Plagioclase - 11.78 - -
Diopside - 3.09 - -
Augite - 0.79 - -
Smectite - 40.77 - -
*Sample was slightly weathered already.
The Smectite content in the Codrington samples increases as the Plagioclase and
Augite content decrease, this suggests the decomposition of primary minerals such as
Plagioclase and Augite to a secondary mineral Smectite, see Table 17. The highest
Smectite content is in the top residual basalt at 51.19%, this horizon also has the lowest
Plagioclase content with no Augite.
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The Smectite contents in the residual basalt at Siloam are less than two orders of
magnitude from each other with a min of 40.18% and max of 53.28% with one sample
containing no Smectite. Although this sample does contain high amounts of Chlorite also
a type of secondary mineral. Either smectite is the dominant secondary mineral to form
from these minerals or all the other clay minerals have been transported out of the profile
in each horizon which seems unlikely.An incongruous mineral occurring in the residual
basalt at Siloam is the presence of Epidote in low to relatively high quantities of
minimum 5.10% and maximum of 23.57%. Epidote is mostly formed by metamorphism
and hydrothermal activity. The individual data can be viewed in Tables C6 and C7,
Appendix C.
5.3 Engineering Parameters
5.3.1 Atterberg Limits
Table 18 below portrays the average and standard deviation values of the
Atterberg Limits for the residual horizons of the study sites. The average for the
Mooiplaas site is the collective residual basalt horizons for the site’s 2 main profile types
viz. NBProfile 2A and NBProfile 2B. This was done since the individual averages for
these profile types were very similar, individual data can be viewed in Appendix A.
Table 18: Residual horizon Atterberg Limit averages from all sites.
Residual horizon
Site Nhlowa Mooiplaas Roedtan Siloam Codrington
Average
Standard
Deviation Average
Standard
Deviation Average
Standard
Deviation Average Average
No Data
% Clay 13,20 4,09 4,88 2,70 3,00 1,00 14,83 9.26
% Silt 34,60 9,10 18,25 7,34 12,33 2,31 20,67 7.79
% Sand 36,40 9,50 41,75 11,72 36,33 6,66 32 13.25
% Gravel 15,20 16,04 35,50 17,19 48,00 8,72 27,5 21.80
Liquid Limit
(%) (LL) 48,60 11,67 50,63 8,90 31,33 2,08 53,67 7.79
Plasticity
index (%) (PI) 23,20 6,02 21,50 4,31 13,33 4,04 28,5 5.47
Linear
shrinkage (%)
(LS)
11,30 3,03 10,25 1,83 5,83 1,26 12,33 1.63
Table 19 indicates that the Siloam site has the highest average clay percentage
followed by the Nhlowa site. Although for Siloam this high average is created by one
very high clay percentage value from TP08 at 0.70-1.10, with a clay content of 33%.
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When this value is excluded the average clay percentage of the Nhlowa site is
11.20%. Aside from this the highest fines content (clay and silt) is present at the Nhlowa
site. The Mooiplaas and Roedtan sites both have lower fines content and higher gravel
and sand than the Siloam and Nhlowa sites. The Nhlowa and Siloam sites are located in
the more humid areas of South Africa with similar climatic environments, the climatic
N-value for Nhlowa is between 2.62-2.78 and the N-value for Siloam is 1.60-2.21.
The aforementioned range of N-values promotes decomposition or chemical
weathering. This correlates to the high fines content encountered at these sites as well as
the high liquid limit and plasticity index. Considering the standard deviations, maximums
and minimums of the two site, they portray very similar values for these properties.
Mooiplaas and Roedtan falls in similar climatic environments with similar
rainfall and evaporation, the N-value for Mooiplaas is between 3 and 4 and for Roedtan
between 3 and 5. These N-values indicate a sub-arid environment where
disintegration/physical weathering would be more dominant with some form of
decomposition still taking place. This correlates with the low fines content and high
gravel and sand encountered.
The Roedtan site is slightly more arid (closer to N=5) which is portrayed in the
higher coarse material and lower fines compared to the Mooiplaas site. In contrast to be
located in a more arid environment, the Mooiplaas site has similar LL and PI to the
Nhlowa and Siloam sites with 50.63% and 21.50% respectively. This could be attributed
to the high smectite clay content present in the residual basalt from the Mooiplaas site,
as well as from the powder calcrete (as calcite and magnesian is at 21.64%), calcrete
characteristically having high LL and PI with low swelling clays.
The higher smectite and in turn higher LL and PI could be attributed to the lower
evaporation rate present at the Mooiplaas site (1700-1900mm) compared to the Roedtan
site (1800-2000). The Roedtan site has the lowest clay content and PI which would be
expected in this more arid site.
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Table 19: Completely to highly weathered basalt Atterberg Limit averages.
Completely to highly weathered basalt
Site Nhlowa Roedtan Codrington
Depth (m) Average
Standard
Deviation Average
Standard
Deviation
No DATA
Origin
% Clay 4,5 0,71 0,6 0,89
% Silt 17,5 2,12 5,2 0,84
% Sand 48,5 12,02 27 4,47
% Gravel 30 14,14 67,2 5,59
Liquid Limit (%) 44 11,31 30,8 4,71
Plasticity Index (%) 19,5 7,78 10,4 2,7
Linear shrinkage (%) 9,5 3,54 4 1,22
Table 19 above portrays the Atterberg Limits for the completely to highly
weathered basalt horizons between the Nhlowa and Roedtan sites. These two sites
respectively represent a high rainfall/humid area and a low rainfall more arid area. As
would be expected the Nhlowa site, a humid area, has higher fines, LL, LS and PI than
the Roedtan site a more arid area. The liquid limit and plasticity index for the completely
to highly weathered basalt of the two sites are relatively similar to the values for the
residual basalt horizon presented in Table 18: Residual horizon Atterberg Limit averages
from all sites., differing by 3% to 4%.
5.3.2 Compaction data
Table 20 and Table 21 below portrays the CBR and Mod. AASHTO compaction
data for the Sibasa basalts at Siloam and the Springbok Flats basalts at Roedtan. All the
horizons tested for the Siloam site classify as a G9 according to the COLTO classification
system (COLTO, 1998). This is due to the high PI and very low compactive strength of
the material.
In contrast to the Siloam site, the completely to highly weathered basalt and
calcified residual basalt both classify as G7 material according to the COLTO
classification system. This is attributed to the low PI contents and good compaction
strength of the material on the Roedtan site. The highly weathered basalt at Roedtan
classifies as a G8 according to the COLTO classification system (COLTO, 1988). This
is due to the low compactive strength of the material at 93% and 95% even though the PI
is relatively low and acceptable.
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Table 20: Mod. AASHTO and CBR test results for the Sibasa Basalts at Siloam.
Test
pit
no
Sample
depth
(m)
Material
description PI
MOD. AASHTO CBR VALUES at% Mod.
AASHTO Soil Classes
MDD
(kg/m3)
OMC
(%) Swell% 90 93 95 98 100 USCS AASHTO COLTO
TP01 1.50-
2.50
Residual
basalt 21 1880 12,9 1,4 4 5 6 7 8 SC A-7-6 (5) G9
TP02 1.10-
1.60
Reworked
pebble
marker/
residuum
30 1993 11,5 1,2 4 5 5 6 7 GC A-2-7 (3) G9
TP06 1.00-
2.00
Reworked
pebble
marker/
residuum
32 1836 12,3 6,1 1 2 2 2 3 SM A-2-7 (4) G9
MDD – Maximum Dry Density; OMC – Optimum Moisture Content, PI – Plasticity Index
Table 21: Mod. AASHTO and CBR test results for the Springbok Flats basalts at
Roedtan.
Test
pit no
Sample
depth
(m)
Material
description PI
MOD. AASHTO CBR VALUES at% Mod.
AASHTO Soil Classes
MDD
(kg/m3)
OMC
(%) Swell% 90 93 95 98 100 USCS AASHTO
COLTO
TP04 1.50-
2.30
Completely
to highly
weathered
basalt
10 2120 10,6 0,0 27 33 38 61 86 SW A-2-4 (0)
G7
TP05 0.50-
1.10
Calcified
residual
basalt
14 2039 10,6 0,0 24 30 35 48 61 SC A-2-6 (0)
G7
TP07 1.00-
2.00
Highly
weathered
basalt
12 2057 10,3 0,0 8 10 12 15 17 SP-SM A-2-6 (0)
G8
MDD – Maximum Dry Density; OMC – Optimum Moisture Content, PI – Plasticity Index
From the data presented here the presence of the abundant calcrete in the calcified
residual horizon shows that it aids in achieving high compaction and CBR values similar
to the completely to highly weathered horizon at the Roedtan site.
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6. SUMMARY
This chapter will provide a short summary on the results acquired during this
study. This was incorporated owing to the large data set from multiple sites.
The investigation covered 5 different low relief basalt sites for different rainfall
intensities and evaporation rates, underlain by different geological lithologies. Two sites
in high rainfall areas and three in low rainfall areas were investigated. The first high
rainfall area is, the Southern Basalt Research Supersite (Nhlowa) in the Kruger National
Park which represents the Lebombo Group basalt, with an average precipitation of
610mm/annum and evaporation of 1600-1700mm/annum. The second high rainfall site
is in Siloam which represents the Sibasa Group basalt, with a precipitation range of 680-
810mm/annum and evaporation of 1300-1500mm/annum. These two sites classify as
humid to sub-humid area with their climatic N-value as, Nhlowa site N=2.62-2.78 and
Siloam N=1.60-2.20.
The first low rainfall area is the Northern Basalt Research Supersite (Mooiplaas
site) which also represents the Lebombo Group basalt, with an average precipitation of
480mm/annum and evaporation of 1700-1900mm/annum. The second site is at Roedtan
which represents the basalt in the Springbok Flats Basin, with a range of 344-
470mm/annum and evaporation of 1800-2000mm/annum. The last site is at Codrington,
also on the Springbok Flats which has a precipitation range of 400-634mm/annum and
evaporation of 1700-1800mm/nnuma. These sites classify as sub-humid to slightly arid
conditions with their climatic N-value aa, Mooiplaas N=3.54-3.95, Roedtan N=3.00-5.00
and Codrington N=2.68-4.50.
Regionally the most noticeable difference between these sites, particularly
between the rainfall intensity groups, are the different pedocrete formations present. The
high rainfall and low evaporation sites contain ferricrete whereas the lower rainfall and
higher evaporation sites are dominated by calcrete. The humid areas also experienced
more chemical decomposition resulting in higher clay contents with higher liquid limit
(LL), linear shrinkage (LS) and plasticity index (PI) values. The sub-humid to arid areas
experienced more physical weathering or disintegration which results in coarser soil
textures and lower Atterberg Limit values.
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These two rainfall intensity groups experienced different mineralogical changes
and element exchanges due to the different climates they are located in and different
underlying geological lithologies.
6.1 Geology and Rock mineralogy
According to Duncan and Marsh (2006) the Nhlowa site is underlain by the Sabie
River Formation and depicted as tholeiitic (olivine poor) basalts. The Mooiplaas site is
in turn underlain by the Letaba Formation which is described as picritic (olivine rich)
basalt. According to Marsh (1984) the basalts in the Springbok Flats Basin is closely
related to the Drakensburg Formation, although compositionally and petrographically
more to the Sabie River Formation.
With the use of the available rock sample XRF averages and plotting them on an
AMF diagram, the Nhlowa site basalts plotted on the boundary of tholeiitic and calc-
alkaline. The Mooiplaas site plotted as calc-alkaline and the Springbok Flats basalt
sample from Codrington plotted as tholeiitic, Figure 25. The Springbok Flats basalt
sample plotting as tholeiitic correlates with Marsh (1984) to be compositionally and
petrographically similar to the Sabie River formation, which is described as tholeiitic
(olivine poor) basalts, no olivine was present in the slightly and highly weathered basalts
from Codrington.
Even though the northern basalts in Mooiplaas are described as olivine rich, only
two of the six rock samples contained the Mg rich olivine mineral Forsterite. The Nhlowa
site does not contain any olivine mineral as described by Duncan and Marsh (2006). The
iron and alkali contents of the two sites are very similar; with the Fe2O3 content of the
Mooiplaas and Nhlowa sites at 12.29% and 12.43% respectively. The alkali content
(Na2O and K2O) of Mooiplaas at 3.81% and 1.56% and Nhlowa at 3.32% and 2.16%.
This only large difference is the average Mg content, whereby in the northern basalts it
is higher than the southern basalts at 8.38% to 5.22% respectively. This places the
Mooiplaas basalts in the calc-alkaline region of the AMF diagram and the southern
basalts on the boundary.
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The XRF analyses indicate that the Ca content of the rock samples from the
northern and southern basalt sites are very similar with the average Ca content at 8.81%
and 7.71% respectively. With the Fe and Ca concentrations very similar between the sites
similarly with the Na and K contents they originate from different mineral assemblages
and types of minerals between the two sites.
For example the northern basalts contain the pyroxene mineral Augite
((Ca,Na)(Mg,Fe,Al)(Al,Si)2O6) in all 6 samples, with an average of42.15% and standard
deviation of 13.61%. The southern basalts do not contain Augite but does have Diopside
(Ca(Mg,Fe)Si2O6) with an average of 15.65% and standard deviation of 22.13% which
contributes different amounts and types of elements as mentioned above. Similarly, the
northern basalt rock samples contain minerals which the southern basalt rock samples do
not contain. This would be tectosilicates such as Analcime (NaAlSi2O6·H2O), Natrolite
(Na2Al2Si3O10·2H2O) and the already mentioned Mg Olivine endmember Forsterite.
These minerals are also not constant in the results from the northern basalt rock samples,
certain samples lacking these minerals. The same can be said for the concentrations of
Plagioclase, Orthoclase, Magnetite, Hematite and Hornblende.
The basalt rock sample from the Springbok Flats basalt in Codrington also contain
Augite (19.59% and 24.73%) although no Olivine, Diopside or Microcline albeit does
contain Plagioclase at 43.95%. The Springbok Flats basalt also has extremely low K2O
at 0.46% and slightly higher Na2O at 2.12% and Fe2O3 at 11.09%. Although it has the
highest CaO content at 9.86%.
The secondary alteration mineral Smectite was already present in the Springbok
Flats highly weathered basalt and slightly weathered basalt samples at 35.85% and
23.96% respectively. This indicates that weathering and alteration has already started and
could explain why the Augite mineral is so much less than the Mooiplaas basalts.
Smectite was only present in one sample of the Mooiplaas basalts at 56.29% this sample
had the lowest Augite content at 26.34%, the Nhlowa site did not contain any Smectite.
This indicates that the mineral Augite when weathered is predominantly altered to
Smectite and can aid in the determination of the extent of weathering.
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6.2 Profile development and weathering
6.2.1 Profile differences
The most pronounced difference between the sites are the distinct different
pedogenic formations present. This would be calcrete at the Mooiplaas, Roedtan and
Codrington sites with ferricrete at the Nhlowa and Siloam sites. The Nhlowa site is
slightly more diverse in different profile types than the Mooiplaas site. The Siloam,
Roedtan and Codrington sites only have 1 profile type due to the close proximity and
similarity of the test pits.
The high rainfall and low evaporation sites of Nhlowa and Siloam experienced
dominantly chemical decomposition, both these sites located in areas of N<3. The
Nhlowa site has 4 profile types with the following horizon assemblages, Table 3 to Table
6:
1. SBProfile 1: Colluvium-residual basalt – highly weathered basalt,
2. SBProfile 2: Reworked residual basalt – scattered residual basalt – highly or
moderately weathered basalt,
3. SBProfile 3: Residual basalt – highly weathered basalt,
4. SBProfile 4: Alluvial profile.
The profiles are mostly characterized by the presence of more fines than coarse
material excluding the highly weathered basalt gravel fragments excavated. Ferricrete
nodules are mostly found in the residual basalt horizon although not in high
concentrations or fully developed, some ferruginization was visible on the highly
weathered basalt gravel excavated.
One profile type was given to the Siloam site with the sequence of colluvium –
reworked pebble marker/residuum – residual basalt. The residual basalt horizon has a
fines content of approximately 35%. Ferricrete nodules were not present in every test pit
and was only located in the reworked and residual basalt layers.
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The Mooiplaas site was divided into 3 profile types with the following horizon
assemblages, Table 7 to Table 10:
1. NBProfile 1: Colluvium – residual basalt,
2. NBProfile 2A: Reworked residual – residual basalt,
3. NBProfile 2B: Reworked residual – residual basalt – highly weathered basalt,
4. NBProfile 3 the alluvial profile.
The majority of the horizon characteristics from the profiles of the Mooiplaas site
are very similar resulting in the NBProfile 2 split of 2A and 2B. These two profile types
are seemingly identical with minor differences in their horizon characteristics and
profile succession, termination occured in different horizons due to refusal on calcrete
nodules/concretions and highly weathered basalt. Although if refusal did not occur
profile succession would seemingly be similar to identical. The profiles from the
Nhlowa site are not as alike to each other in profile succession as the Mooiplaas site,
although analogous horizon characteristics are present as well as a similar profile
succession. Calcrete formations in the Mooiplaas profiles are concentrated in the
residual basalt horizon although also present in lesser extent in the reworked residual
basalt horizon. Silt and sand is the main soil texture across the reworked and residual
basalt horizons with high gravel content from hard calcrete concretions.
Roedtan is the site with the lowest rainfall and highest evaporation rate and has a
dominant gravel and sand texture in the residual basalt layer and weathered basalt
horizons when excavated with a TLB. The basic profile horizon sequence encountered
was colluvium – calcified residual basalt - completely weathered basalt – highly
weathered basalt (with patches of moderately weathered basalt in the latter two horizons).
The residual basalt horizon is specifically labelled as calcified due to the abundance of
calcrete formations (nodules, concretions and streaks) present. The high gravel content
in the residual basalt horizon is attributed to the calcrete nodules and concretions as well
as weathered basalt gravel. This indicates the dominant presence of physical
disintegration over chemical decomposition with the fines content at less than 5%.
Only one profile was described at Codrington to serve as extrapolative data for
the Springbok Flats basalt. The profile encountered had two residual basalt horizons
underlain by a highly weathered basalt layer.
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The top residual basalt horizon contained calcrete nodules and concretions with
a clayey sand texture whereas the underlying residual basalt horizon had no calcrete and
was clay dominant.
6.2.2 Element exchange
The most pronounced difference in element exchange between the Mooiplaas and
Nhlowa site is the Fe and Ca contents. The Nhlowa site has approximately twice as much
Fe in the residual basalt horizon at an average of 16.21% compared with the Mooiplaas
site at an average of 7.94%, this is attributed to the presence of ferricrete in the Nhlowa
profile. The average Fe content of the Nhlowa site increases from the parent rock at
12.43% up to the colluvial layer with 18.37%. The reverse occurs at the Mooiplaas site
where average Fe content is decreased from the parent rock at 12.29% to 7.94% in the
residual basalt layer, the reworked and colluvial layers are similar to the highly weathered
basalt layer at around 9.50%.
The residual and highly weathered basalt of the Mooiplaas site has a higher
average Ca content of 11.98% and 13.48% respectively than the parent rock at 8.81%.
The highest Ca concentration is in the highly weathered basalt horizon is likely attributed
to the Ca in the rock together with the calcification in the highly weathered rock structure.
Calcium concentrations drop below the parent rock’s level at the reworked residual basalt
and colluvial horizons, these concentrations are lower than the Fe content in the same
horizons which indicates that Ca is readily mobilized from the system by erosion. The
average Ca content of the Nhlowa site decreases from the parent rock at 7.71%, highly
weathered basalt 6.72%, residual basalt 5.01% then drastically to the colluvial layer at
0.80%.
The high Fe content range in the residual basalt horizon of the Siloam site
(14.45% to 17.18%) is similar to that of the Nhlowa site of 13.79% to 18.74%. Siloam
has similar low and high ranges of Ca contents to the Nhlowa site, with 3.20% to 10.05%
for Siloam and 1.20% to 10.70% for Nhlowa. The Codrington site has slightly higher Fe
content in the residual basalt horizon of 9.07% and 14.80% compared to the Mooiplaas
site with an average 7.94%, although the average Fe in the highly weathered basalt
horizons are very similar at 10.70% for Codrington and 9.57% for Mooiplaas.
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The Codrington site has a slightly similarity to Mooiplaas where increase in the
Ca content occurs from the slightly weathered basalt to the highly weathered basalt.
Although no XRF information was gathered at Roedtan in order to compare the Ca
contents, based on just visual inspection, Roedtan would have the higher Ca content
compared to Mooiplaas.
The Mooiplaas site has lowest average Fe content at 7.94% in the residual basalt
horizon with the highest at Nhlowa with 16.21%. The average Fe content for Siloam and
Codrington site are between these two sites, with Codrington at 11.94% and Siloam at
14.45%. The Mooiplaas site has the highest average Ca content in the residual basalt
horizon of all the sites at 11.98% followed by the Codrington site with 7.42%, the Siloam
site with 6.35% and the Nhlowa site with the lowest at 5.01%.
Moon and Jayawardane (2004) and Bih Che et al. (2012) indicated that in the
initial weathering of basaltic rock from parent to slightly weathered to highly weathered
rock etc. a loss and depletion of the main elements of Mg, Fe and Ca are experienced.
Both in the Mooiplaas and Nhlowa site a depletion of Mg is noticed although the Ca and
Fe contents differ dependant on the site. The average Ca and Fe contents in the parent
rocks of the Mooiplaas is 8.81% and 12.29% respectively and 7.71% and 12.43% at the
Nhlowa sites respectively. Even though the parent rocks of these two sites have similar
starting Ca and Fe contents their profile concentrations follow opposite enrichments and
depletions. The Ca content at the Nhlowa site steadily decreases from parent rock to
residual basalt whereas the Fe content drastically increases by approximately 4%. The
opposite occurs at the Mooiplaas site where the Fe content decreases (as sharply as it
increases at the Nhlowa site) and the Ca content increases from the parent rock to the
highly weathered and residual basalt horizons.
The Y and Zr content in both sites show an increase and decrease from the parent
rock upwards through the profile. Although some standard deviations are large 10ppm to
14ppm for Y and 100ppm to 200ppm for Zr a mobilization of these elements are still
occurring from the parent rock through the profile. The Zr content at Codrington
increases from 105ppm for the slightly weathered basalt to 202ppm at the top residual
horizon. As for the Siloam site the average an increase if Y from the parent rock to
residuum.
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TP08 at Siloam indicates an overall increase in Y of 27ppm, 23ppm to 32ppm
upwards through the profile sampled from different depths. The same occurs with the Zr
content where it decreases from 119 pp to 115ppm and then increases to 184ppm. This
indicates the mobility of both elements, previously thought to be immobile. In TP05 an
increase of both Y and Zr also occurs, 29ppm to 32ppm and 156ppm to 167ppm
respectively.
6.2.3 Mineralogical changes
The following mineralogical changes were noticed that occurred with these
elemental changes. The parent rock from the Mooiplaas site contained only the pyroxene
mineral Augite and the Nhlowa site only Diopside. The weathered profile horizons of the
Mooiplaas site in contrast to the rock samples contains more Diopside in total of
individual samples than Augite. Also conflicting with the parent rock concentrations is
the residual basalt layers of the Mooiplaas site, which contains Diopside in 12 of the 17
samples at a minimum of 3.86% and maximum of 24.20%. Diopside was also present in
the highly weathered basalt of the Mooiplaas site.
The Augite and Diopside concentrations collectively in the weathered horizons
are notably lower than the Augite concentrations in the parent rock. No Augite was
encountered in the Nhlowa site and the Diopside content decreased greatly from the
parent rock to the residual basalt horizon, 31.30% to 4.75% respectively, with Diopside
not present in every sample.
Smectite is present in almost every sample of the weathered horizons from the
Mooiplaas site. The Nhlowa site does not have this high occurrence of the clay mineral,
with Smectite of 18.22% in only one sample. For the Mooiplaas site the reworked
residual basalt horizon contains the most Smectite, indicating the most active weathered
horizon. The residual basalt and highly weathered basalt contain very similar amounts
based on the averages and standard deviations but still less than the reworked residual
basalt. The minimum and maximum percentages of these horizons are (not including
0.00%): Reworked residual basalt 38.83% and 65.92%; Residual basalt 22.05% and
57.47%; highly weathered basalt 25.85% and 52.43%.
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The samples from the Nhlowa site lacks any other clay minerals except the
phyllosilicate mineral chlorite. Based on the results, the Smectite clay mineral results
from the weathering and breakdown of Augite, Plagioclase, Magnetite, Hematite,
Forsterite and the tectosilicates Analcime and Natrolite. It was observed that the Smectite
content increases as the content of these minerals decrease. This is especially notable at
Mooiplaas with Augite weathering to Smectite. From parent rock to highly weathered
rock the Augite content drastically decreases (42.15% to 6.99%) whereas the Smectite
content increases drastically (9.38% to 36.89%). The Nhlowa shite which does not
contain any Augite results in very few amounts of Smectite. The tectosilicates mentioned
are only present in the northern basalt parent rock mineral assemblages and not in the
southern basalts.
The presence of pyroxene in the residual basalt at Siloam is scarce, with one
sample containing Diopside and two with Augite. No Diopside is present in the
Codrington samples although the Augite content decreases from the slightly weathered
basalt of 24.73% to the bottom residual basalt of 14.52%, the top residual basalt contains
no Augite. The Plagioclase content also decreases in the Codrington sample from very
high percentage to very low.
The slightly weathered basalt contains 43.95% Plagioclase which decreases to
6.96% in the top residual horizon. The Smectite content in conjunction with this increases
as the Plagioclase and Augite content decreases further indicating the transformation of
these primary minerals to Smectite during decomposition. The Smectite content in the
slightly weathered basalt is 23.96% and 51.19%. in the top residual horizon.
The Plagioclase in the residual basalt at Siloam is very low at 3.20% to 26.45%
compared with very high Smectite contents of 40.18% to 53.28%. Siloam also has much
more Chlorite content although low when paired with Smectite, the Chlorite ranges from
3.37% to 8.98%. The one sample that does not have Smectite contains higher Chlorite
content at 27.71% and this sample in turn has no Augite or Diopside and very low
Plagioclase at 6.53%.
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The release and mobilization of elements in different stages are a result of an
amalgamation of different factors. These factors are influenced by different weathering
rates and mineral breakdowns which is attributed to the high diversity of minerals present
between rocks of different climatic environments.
6.3 Engineering Geology
The Nhlowa and Siloam sites have the highest fines content which correlates with
the humid environment they are located in. The average clay and silt content of the
Nhlowa site is 13.20% and 34.60%, the Siloam site has slightly higher clay content of
14.83% although a lower silt content 20.67%. This relates to the expected high LL, PI
and LS of the sites. the Nhlowa site averages are 48.60%, 23.20% and 11.30%
respectively. The Siloam site has similar values of 53.67%, 28.50% and 12.33%
respectively.
The drier more sub-humid to slightly arid environments of Mooiplaas and
Roedtan do have lower fines content. With the clay and silt at Mooiplaas at 4.88% and
18.25% and at Roedtan at 3.00% and 12.33% respectively. These sites are dominated by
high sand and gravel contents, the sand and gravel in excess of 35%. The Roedtan has
the highest gravel content at 48% and Mooiplaas the highest sand at 41.75%. The
Atterberg limits for these two sites are low with a PI of 13.33% at Roedtan. Although the
Mooiplaas site has similar LL, PI and LS to the more humid Nhlowa and Siloam sites
despite having much lower clay and higher sand and gravel contents than them. This
could be attributed to the high calcrete content containing Palygorskite paired with the
high smectite present in the horizon. The higher rainfall and lower evaporation compared
to Roedtan could also aid in creating this skewed effect.
The LL, PI and LS for the completely to highly weathered basalt for the Nhlowa
and Roedtan sites are very similar to their residual basalt values, only being slightly less.
The fines content for Nhlowa are still relatively high with clay of 4.50% and silt at
17.50% whereas the Roedtan site has almost no clay at 0.60% and very low silt of 5.20%.
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The better compaction characteristics are found at the sub-arid area Roedtan when
compared to the humid area of Siloam. The calcified residual basalt and completely to
highly weathered basalt at Roedtan classifies as G7 material according to the COLTO
classification system. This material had low PI of 10 to 14 with adequate compressive
strength at 95% Mod. ASSHTO. Compared to the Roedtan the residual basalt material
of Siloam only classifies as G9, this rating is supported by the high PI of 21 to 32 and
low compressive strength of the material.
7. Conclusion
With the completion of this study a better understanding of the weathering trends
and soil development for low relief basalts have been achieved. Even though low relief
basalts do not contain distinct noticeable topography, such as crests, mid-slopes and foot-
slopes, differences in profile development and weathering are influenced by the flat lying
nature and climatic aspects.
7.1 Profile development
The research sites were naturally divided into high rainfall and low evaporation
sites such as for Nhlowa and Siloam, and low rainfall high evaporation sites for
Mooiplaas, Roedtan and Codrington.
• The vertical profile succession from the Mooiplaas site is more uniform than those on
the Nhlowa site. Although analogous horizon characteristics are present to provide
similar profile successions such as reworked residuum – residual basalt – highly
weathered basalt.
• The Nhlowa site portrayed a more sporadic presence and absence of horizons in the
profile succession than the Mooiplaas site. This indicates higher weathering variability
across the site due to the higher rainfall and lower evaporation.
• Ferricrete nodules are mostly found in the residual basalt horizon although not in high
concentrations or fully developed, some ferruginization was visible in the highly
weathered basalt gravel.
• As a result of lower rainfall and higher evaporation the Mooiplaas site has a very
uniform profile succession across the site, this results in the NBProfile2 type split into
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
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2A and 2B. These two profile types are seemingly identical with minor differences in
their horizon characteristics and profile succession, termination occurred in different
horizons due to refusal on abundant calcrete formations or highly weathered basalt. It
reasonably to assume that if refusal did not occur profile succession would seemingly
be similar to identical.
• Silt and sand is the main soil texture for the Mooiplaas site across the reworked and
residual basalt horizons with high gravel content resulting from hard calcrete
concretions.
• Calcrete formations in the Mooiplaas profiles are concentrated in the residual basalt
layer although also present in the reworked residual basalt layer in lesser extent.
• The high rainfall sites of Nhlowa and Siloam have, as expected due to similar climatic
environments, very similar profile horizon successions with similar high fines
contents. Ferricrete was also present at both sites although not constant throughout the
profile and across the site.
• At Siloam ferricrete nodules were not present in every test pit and was only located in
the reworked and residual basalt layers.
• Both Roedtan and Mooiplaas have low rainfall and high evaporation although the
effect of physical disintegration and lack of chemical weathering is much more
noticeable at Roedtan than Mooiplaas where some chemical weathering is still present.
Furthermore, the Roedtan profile is dominated by a very thin residual horizon before
continuing to highly weathered rock.
• This is also evident in the lower fines and higher gravel content throughout the profiles
at Roedtan compared to the Mooiplaas site.
• The degree of calcification present at Roedtan is also the most pronounced and can be
attributed to having a lower rainfall and higher evaporation compared to Mooiplaas.
• A specific trend noticed between the sites are that the high rainfall and low evaporation
sites, Nhlowa and Siloam, contain ferricretes in the profiles.
• The low rainfall and high evaporation sites, Mooiplaas, Roedtan and Codrington
contain calcrete with the more arid site Roedtan containing the highest calcrete content.
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➢ The above two statements agree with the generalization made with Weinert’s N-value
that sub-humid areas (N=2) preferentially form ferricretes and sub-arid to arid areas
(N=5) form calcrete (Brink, 1979 and 1985) and (Netterberg 1969 and 1971 cited in
Brink, 1985).
➢ The above mentioned was also noticed in the enrichment and depletion of Fe and Ca in
soils from these sites.
7.2 Element analysis
The elemental exchange focus for weathering from parent rock to residual soil
was placed on specific major elements viz. Na, K, Ca, Fe, Al and Mg. As well as specific
elements and trace elements previously thought to be immobile, Y, Zr and Ti.
➢ Moon and Jayawardane (2004) indicated in their study that a loss in major elements
(Mg, Fe, Ca, Na) occur with a significant decrease from fresh to moderately weathered
rock and smaller losses to residual soil.
• Only Na and Mg indicated a decrease in concentration from fresh rock to residual soil
in all the study sites, Na being the only element that showed a large decrease in
concentration from fresh to weathered rock.
• In contrast to the study of Moon and Jayawardane (2004), the high rainfall sites
(Nhlowa and Siloam) experience an increase in Fe content and decrease in Ca content.
The reverse occurs in the lower rainfall sites (Mooiplaas and Codrington) where Ca
increases, and Fe decreases from fresh to weathered rock and/or residual soil.
• Although, this still indicates mobilization of the major elements in and out of the
system with respect to enrichment and depletion of the elements, and not just depletion
as with the case in the study of Moon and Jayawardane (2004).
➢ Certain elements and trace elements such as Ti, Y and Zr have thought to be immobile
during the alteration and weathering of crystalline basalt.
• Mobility of all three these elements have been noted in all the study areas.
• The Y content both indicates a depletion and enrichment between the sites and
horizons. At Mooiplaas Y and Zr portrays a slight depletion, whereas at Nhlowa an
increase and decrease of Y content occurs from parent to highly weathered rock and
then residual soil, Zr is locally enriched or depleted.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
105
• The aforementioned is similar to the study of Hill et al. (2013) in northeast Ireland
which experienced a marked decrease of Y and increase of Zr, where Zr is locally
depleted.
• At Siloam and Codrington, a decrease then increase in Y occurs, with Zr at Codrington
increasing upward through the profile. Bih Chi et al. (2012) noticed during their study
on basalt in the humid-tropics in SW Camaroon an increase in Yttrium through the
profile as well.
• Bih Chi et al. (2012) experienced notable mobility of Ti aand Zr in their study where
Hill et al. (2013) noticed an increase in Ti and Zr with laterite formation.
• The abovementioned trend was also noted at Nhlowa having ferricretes with a slight
increase in Ti and Zr content. Although Ti content showed a decrease at Mooiplaas
upward through the profile.
7.3 Mineralogy
The main focus for the mineralogical aspect between the sites were the link
between primary and secondary minerals. Where decreases in primary mineral content
and an increase in secondary minerals especially smectite clays indicate weathering
extent.
➢ Houston and Smith (1997) determined the degree of alteration of basalt by comparing
a primary mineral (Plagioclase) in basalt to a weathered product or secondary mineral
(Smectite) in basalt from New South Wales Australia.
• The aforementioned was also observed in the samples from the study sites that a lower
Plagioclase concentration occurred upward through the profile with an increase in
smectite. A low Plagioclase content in a sample also correlated with a high Smectite
content, compared to the original concentrations in the parent rocks.
• Although, the decrease in Plagioclase content was not significant or proportionate to
the increase in smectite concentrations, e.g. the Nhlowa site had a decrease in
plagioclase content (present in every sample) with only some smectite detected in
scattered samples, even in the residual soil.
• High smectite content is however present in the Mooiplaas and Codrington site with a
marginal lower Plagioclase content.
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• The dramatic increase in smectite content at these two sites were mostly attributed to
the weathering of Augite. This was observed with the drastic decrease of Augite
content from parent to highly weathered rock paired with a high increase of Smectite.
• If a high Smectite content was present together with Augite in the sample the
Plagioclase content would be less than the overall average between the samples.
Indicating a combination of the weathering of Plagioclase and Augite to produce
Smectite with Augite preferentially weathering.
➢ The previous statement’s occurrence was also described in the studies by Moon and
Jayawardane (2004) on the Karamu Basalts in New Zealand and by Hill et al. (2013) in
northeast Ireland. Where they found that after initial weathering, Fe-rich Smectites are
the replacement product of weathered Olivine and Augite and Al-rich Smectites the
replacement product of weathered Plagioclase. This indicates a combination of the
weathering of Plagioclase and Augite to create Smectite with Augite weathering
preferentially.
• A similar trend was observed in certain residual basalt samples which has no Augite
and relatively high Plagioclase and high Smectite, where in samples with low Augite
content had less Plagioclase but still high Smectite content.
• The rock samples from the Nhlowa site indicated not to have any Augite in the parent
rock and the Plagioclase did not preferentially weather to Smectite, this is shown by
the very low Smectite content in the samples. Some scattered samples did however
contain Smectite which could point to the possibility of the original rock weathering
to the residual sample containing some Augite and having it favourably weather over
Plagioclase.
➢ The study of Bih Chi et al. (2012) on basaltic soils in humid tropic climates in south-
western Cameroon, concentrated on the weathering of Olivine, Pyroxene, Amphibole
and calcic Plagioclase as the principal minerals weathering from fresh rock to soil.
• In all the study sites, very little to no Olivine and Amphibole were present, this meant
that the main weathering minerals here were Pyroxene and Plagioclase. Klein and
Dutrow (2007) commented that Olivine usually occurs as phenocrysts. Also that
Olivine will be very scarce in a sample due to being the most unstable mineral on
surface and weathers preferentially before other minerals.
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107
7.4 Engineering Data
The mechanical tests done were merely to provide engineering property
information on the weathered products of low relief basalts. This was compared to
existing data for the residual soils of Drakensburg and Sibasa basalt Formations in order
to highlight differences or similarities.
➢ Brink, 1983 on pages 156 to 157 provides tables of expected values for residual basalt
of the Drakensburg Formation in Lesotho and the Letaba Formation of the Lebombo
Group in Komatipoort.
• The Mooiplaas site underlain by the Letaba Formation has slightly higher average
Liquid Limit and Plasticity Index than the residual soil at Komatipoort.
• When the low relief high rainfall sites (Nhlowa and Siloam) are compared to the
mountainous and high rainfall environment of the Drakensberg the LL and PI of the
study sites are much higher.
• The average LL and PI in a valley setting below 2 500m in Lesotho are 38.8% and
13% whereas Nhlowa has a much higher LL and PI of 48.6% and 23.20% and Siloam
at 53.67% and 28.5% respectively. This indicates that the weathering intensity on flat
lying basalts are higher than in mountainous and valley settings even with very high
rainfall conditions.
• The only site which has similar LL and PI to the valley setting of the Drakensberg is
Roedtan at 31.33% and 13.33% possibly due to the flat lying nature of the site. A
possible reason to this is that even with low rainfall, water will stay in the rock and soil
long enough to simulate a degree of chemical weathering conditions similar to the high
rainfall and high runoff in a mountain and valley setting.
• At Roedtan the compaction effort at 95% Mod. AASHTO for the calcified residual
basalt is 35 and the completely weathered basalt 38. This is relatively close to the
valley and mountain settings, with values of 45 and 47.
• The LL of 41% to 64% and PI of 21% to 37% for the residual Sibasa basalts at Siloam
very similar to the values provided in Brink (1981) at the Nzhelele dam in Venda, with
a LL of 35% to 62% and PI of 5% to 26%, although closer to the higher values.
• For the residual basalt at Nzhelele dam in Venda, Brink (1981) provides values of 6 to
59 for a compaction effort of 95% Mod. ASSHTO whereas at Siloam values of 2 to 6
was achieved.
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It is not sufficient to only gather information and understand the effect of
weathering of a single setting on a specific rock type. Understanding the effects of
weathering on low relief as well as mountainous basalt in variable climatic conditions
are crucial to comprehend the behaviour of basalt as well as other rock types during the
complex process of weathering. As displayed in this study a moderate shift in climate in
terms of rainfall and evaporation can have far reaching effects on the residual soil
development on basalt. Effects such as substantial differences in pedocrete formation
between high and low rainfall areas to the type of soil formation from very gravelly or
dominated by fines are noticeable even for similar low relief areas with slight
mineralogical differences.
Future studies should set out to investigate both low and high relief areas in
different climatic conditions together in order to produce collective information with the
intention of creating possible new investigation techniques that are time and cost
effective.
8. Acknowledgements
First and foremost, I would like to thank SANparks for such an unbelievable
opportunity to conduct an investigation in the magnificent Kruger National Park. It is an
extremely rare opportunity, and experience which I will never forget. Secondly to my
supervisor Prof. Louis van Rooy for seeing the potential in me to be able to undertake
such an investigation, as well as for all the assistance and guidance you gave me during
this challenging MSc. To the Environment and Engineering Geology Honours class of
2012 at the University of Pretoria, and all who assisted me in gathering the data for this
massive investigation, I thank you. Not that spending time in the Kruger National Park
for the data gathering was such a punishment.
Second to last thank you to my mother Engela van Staden for constantly checking
up on my progress with this MSc, just to make sure I was not getting too relaxed and
forgetful. Even more than that, the example she set for me on how to strive forward and
do your utmost best is unmatched and I could not have asked for a better role model.
Lastly, thank you to my wife to be, Gwendylin Lawson, for all your unwavering support,
love and motivation through the good, difficult and “tuff” times. With you by myside I
know I would be able to achieve anything, I lava you very much.
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The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
Appendix A
Grading Analysis and Atterberg Limits
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
Table A1: Grading and Atterberg Limits of the Mooiplaas site for NBProfile 2A and alluvium.
NBProfile 2A
Test pit NB05 NB11 NB19 NB20 NB29
Average Standard
Deviation
NB05 NB11 NB19 NB20
Average Standard
Deviation
NB32 NB32
Depth (m) 0.00-0.25 0.00-0.24 0.00-0.44 0.00-0.44 0.00-0.21 0.44-0.67 0.32-0.58 0.44-0.95 0.44-1.07 0.0-0.24 0.24-0.80
Origin Reworked Residual Basalt Residual Basalt Alluvium
Calcified
Residual
Basalt
% Clay 9 12 16 9 15 12.20 3.27 8 3 9 4 6.00 2.94 20 29
% Silt 27 39 50 34 44 38.80 8.87 14 9 25 29 19.25 9.32 25 20
% Sand 46 45 30 49 36 41.20 7.92 39 34 47 53 43.25 8.42 42 37
% Gravel 18 4 4 8 4 7.60 6.07 40 54 19 15 32.00 18.31 13 15
Liquid Limit (%) 43 48 73 44 63 54.20 13.22 51 44 65 40 50.00 10.98 50 83
Plasticity Index (%) 17 20 37 17 27 23.60 8.53 24 20 29 18 22.75 4.86 22 38
Linear shrinkage (%) 9 11 18 10 14 12.40 3.65 11 10 13 9 10.75 1.71 9 14
PRA A-7-6 A-7-6 A-7-5 A-7-6 A-7-5 - - A-2-7 A-2-7 A-7-5 A-6 - - A-7-6 A-7-5
Unified classification SC ML MH SM MH - - SC SC SM SC - - SC MH
PRA - Public Road Administration; USCS - Unified Soil Classification System
Table A2: Grading and Atterberg Limits of the Mooiplaas site for NBProfile 2B. NBProfile 2B
Test pit NB06 NB33 NB34 NB34 Average
Standard
Deviation
NB06 NB12 NB27 NB34 Average
Standard
Deviation Depth (m) 0.0-0.48 0.00-0.25 0.00-0.30 0.30-0.60 0.40-0.88 0.50-1.48 0.15-0.35 0.60-0.90
Origin Reworked Residual Basalt Residual Basalt
% Clay 13 12 9 7 10.25 2.75 6 1 3 5 3.75 2.22
% Silt 43 31 35 22 32.75 8.73 23 20 9 17 17.25 6.02
% Sand 31 55 40 28 38.5 12.12 37 63 33 28 40.25 15.61
% Gravel 12 2 16 43 18.25 17.52 34 16 56 50 39.00 17.93
Liquid Limit (%) 67 41 50 55 53.25 10.84 61 47 43 54 51.25 7.93
Plasticity Index (%) 31 16 24 26 24.25 6.24 25 17 17 22 20.25 3.95
Linear shrinkage (%) 16 8 11 13 12.00 3.37 12 8 8 11 9.75 2.06
PRA A-7-5 A-7-6 A-7-6 A-2-7 - - A-7-5 A-2-7 A-2-7 A-2-7 - -
Unified classification MH CL CL SC - - SM SM SC SM - -
PRA - Public Road Administration; USCS - Unified Soil Classification System
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
Table A3: Grading and Atterberg Limits of the Nholwa site.
Profile SB01 Profile SB02
Test pit SB02 SB02 SB03 SB16 SB17 SB17 Average
Standard
Deviation
SB03 SB16 Average
Standard
Deviation
SB16
Depth (m) 0-0.12 0.12-0.55 0.24-0.32 0.38-0.65 0.0-0.64 0.64-0.84 0.71-0.94 0.65-1.03 0.65-1.03
Origin Colluvium Residual Basalt Highly Weathered
Basalt Residual
Basalt
% Clay 17 7 18 12 14 15 13.20 4.09 4 5 4.50 0.71 3
% Silt 36 25 43 45 33 27 34.60 9.10 19 16 17.50 2.12 21
% Sand 42 40 37 41 44 20 36.40 9.50 57 40 48.50 12.02 56
% Gravel 5 27 1 2 9 37 15.20 16.04 20 40 30.00 14.14 20
Liquid Limit (%) 33 47 37 43 48 68 48.60 11.67 36 52 44.00 11.31 42
Plasticity Index (%) 14 21 17 21 24 33 23.20 6.02 14 25 19.50 7.78 19
Linear shrinkage (%) 7 9.5 8 11 12 16 11.30 3.03 7 12 9.50 3.54 9
PRA A-6 A-7-6 A-6 A-7-6 A-7-6 A-7-5 - - A-2-6 A-2-7 - - A-2-7
Unified classification CL SC CL CL CL GM - - SC SC - - SC
PRA - Public Road Administration; USCS - Unified Soil Classification System
Table A4: Grading and Atterberg Limits of the Sibasa Basalts at Siloam (Transported).
Test pit TP01 TP03 TP04 TP05
Average Standard
Deviation
TP01 TP02 Average
Standard
Deviation Depth (m) 0.0-0.7 0.0-1.0 0.0-1.0 0.0-0.6 1.0-1.4 1.1-1.6
Origin Colluvium Reworked Pebble Marker/ Residuum
% Clay 8 22 43 33 26.5 15.02 11 11 11.00 0.00
% Silt 14 33 22 28 24.25 8.18 18 15 16.50 2.12
% Sand 35 43 29 37 36.00 5.77 21 22 21.50 0.71
% Gravel 43 2 6 2 13.25 19.92 50 52 51.00 1.41
Liquid Limit (%) 41 44 54 46 46.25 5.56 48 46 47.00 1.41
Plasticity Index (%) 22 23 28 30 25.75 3.86 26 30 28.00 2.83
Linear shrinkage (%) 11 13 13.5 14 12.88 1.31 13 13 13.00 0.00
PRA A-2-7 A-7-6 A-7-6 A-7-6 - - A-2-7 A-2-7 - -
Unified classification GC CL CH CL - - GC GC - -
PRA - Public Road Administration; USCS - Unified Soil Classification System
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
Table A5: Grading and Atterberg Limits of the Sibasa Basalts at Siloam (Residual horizon).
Test pit TP01 TP03 TP05 TP06 TP08 TP08
Average Standard
Deviation Depth (m) 1.5-2.5 1.5-2.0 0.8-1.2 1.0-2.0 0.7-1.1 2.0-2.5
Origin Residual Basalt
% Clay 8 9 11 15 33 13 14.83 9.26
% Silt 32 17 12 15 28 20 20.67 7.79
% Sand 40 20 21 24 33 54 32 13.25
% Gravel 20 54 56 16 6 13 27.5 21.8
Liquid Limit (%) 46 51 49 64 49 63 53.67 7.79
Plasticity Index (%) 21 26 28 32 27 37 28.5 5.47
Linear shrinkage (%) 10 12 13 15 12 12 12.33 1.63
PRA A-7-6 A-2-7 A-2-7 A-2-7 A-7-6 A-7-6 - -
Unified classification SC GC GC SM CL SC - -
PRA - Public Road Administration; USCS - Unified Soil Classification System
Table A6: Grading and Atterberg Limits of the Springbok Flats Basalt at Roedtan.
Test pit TP02 TP02 TP05 TP06
Average Standard
Deviation
TP02 TP04 TP05 TP06 TP07
Average Standard
Deviation Depth (m) 0.0-0.3 0.5-0.9 0.5-1.1 0.4-0.8 1.0-1.5 1.5-2.3 1.5-2.0 1.4-1.8 1.0-2.0
Origin Colluvium Calcified Residual Basalt Completely to Highly Weathered Basalt
% Clay 15 2 3 4 3.00 1.00 0 0 0 1 2 0.60 0.89
% Silt 18 15 11 11 12.33 2.31 6 4 5 6 5 5.20 0.84
% Sand 66 44 32 33 36.33 6.66 32 21 24 28 30 27.00 4.47
% Gravel 1 38 54 52 48.00 8.72 62 75 71 65 63 67.20 5.59
Liquid Limit (%) 24 29 32 33 31.33 2.08 27 27 29 33 38 30.80 4.71
Plasticity Index (%) 10 9 14 17 13.33 4.04 8 10 9 10 15 10.40 2.70
Linear shrinkage (%) 4 4.5 6 7 5.83 1.26 3 3 4 4 6 4.00 1.22
PRA A-4 A-2-4 A-2-6 A-2-6 - - A-2-4 A-2-4 A-2-4 A-2-4 A-2-6 - -
Unified classification SC SC SC SC - - SP-SC SW SP-SC SP-SC SP-SM - -
PRA - Public Road Administration; USCS - Unified Soil Classification System
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
Appendix B
XRF Results
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRF (wt % )
Test pit NB01 NB03 NB30 NB31 NB32
Depth (m) 0.00-0.40 0.00-0.25 0.00-0.38 0.00-0.40 0.00-0.24
SiO2 60.98 56.41 58.70 3.23 51.48 49.80 45.33 48.87 3.18
TiO2 1.61 1.28 1.44 0.24 2.76 2.13 2.06 2.32 0.38
Al2O3 13.16 13.37 13.27 0.15 9.17 7.39 5.34 7.30 1.92
Fe2O3 9.52 9.51 9.52 0.00 11.54 9.54 6.64 9.24 2.46
MnO 0.13 0.17 0.15 0.03 0.15 0.12 0.10 0.13 0.02
MgO 1.77 4.11 2.94 1.65 6.06 8.92 10.13 8.37 2.09
CaO 2.31 4.59 3.45 1.61 4.04 4.32 10.12 6.16 3.43
Na2O 1.35 1.13 1.24 0.15 1.29 0.70 1.30 1.10 0.34
K2O 1.91 1.27 1.59 0.45 1.84 1.45 1.25 1.51 0.30
P2O5 0.10 0.10 0.10 0.00 0.25 0.33 0.16 0.25 0.09
Cr2O3 0.05 0.07 0.06 0.01 0.11 0.09 0.07 0.09 0.02
NiO 0.03 0.04 0.04 0.00 0.06 0.05 0.03 0.05 0.01
V2O5 0.04 0.03 0.04 0.00 0.05 0.04 0.05 0.05 0.00
ZrO2 0.04 0.02 0.03 0.01 0.04 0.04 0.04 0.04 0.00
CuO 0.01 0.00 0.00 0.00 0.01 0.01 0.00 0.01 0.00
LOI 6.00 8.21 7.10 1.56 11.31 14.71 17.70 14.57 3.20
Total 99.01 100.32 99.66 0.92 100.17 99.65 100.31 100.04 0.35
Y 22 16 19.00 4.24 25 23 22 23.75 1.50
Zr 250 149 199.50 71.42 284 236 269 269.25 23.63
ppm
As 0 0 0.00 0.00 0 0 0 0.00 0.00
Cu 78 64 71.00 9.90 95 85 51 77.00 23.07
Ga 16 14 15.00 1.41 14 12 9 11.67 2.52
Mo 2 0 1.00 1.41 1 1 2 1.33 0.58
Nb 10 7 8.50 2.12 17 14 11 14.00 3.00
Ni 201 190 195.50 7.78 415 332 219 322.00 98.38
Pb 9 3 6.00 4.24 1 1 8 3.33 4.04
Rb 63 44 53.50 13.44 42 35 34 37.00 4.36
Sr 188 115 151.50 51.62 265 414 1263 647.33 538.36
Th 0 0 0.00 0.00 0 0 0 0.00 0.00
U 0 0 0.00 0.00 0 0 3 1.00 1.73
W* 49 34 41.50 10.61 20 12 46 26.00 17.78
Y 22 16 19.00 4.24 25 23 22 23.33 1.53
Zn 58 67 62.50 6.36 83 86 50 73.00 19.97
Zr 250 149 199.50 71.42 284 236 269 263.00 24.56
Results indicated with a * should be considered semi-quantitative.
Table B1: Major and Trace Elements, XRF Results at Mooiplaas for the Transported Horizons.
AverageStandard
DeviationAverage
Standard
Deviation
Colluvium Alluvium
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRF (wt % )
Test pit NB06 NB07 NB11 NB11 NB12 NB15 NB17 NB19 NB20 NB22 NB24 NB29 NB31 NB33 NB34 NB34
Depth (m) 0.00-0.48 0.00-0.30 0.00-0.24 0.24-0.32 0.00-0.31 0.00-0.40 0.00-0.30 0.00-0.44 0.00-0.40 0.00-0.47 0.00-0.35 0.00-0.21 0.90-1.20 0.00-0.25 0.00-0.30 0.30-0.60
SiO2 - 44.80 47.52 - 45.40 41.71 57.20 53.11 35.76 57.94 54.67 56.24 43.83 52.55 53.04 48.92 49.48 6.58
TiO2 - 2.75 3.02 - 2.52 2.80 2.80 2.96 2.22 3.40 3.47 3.09 1.82 2.78 3.26 3.27 2.87 1.07
Al2O3 - 6.86 7.44 - 11.20 9.12 9.10 8.78 6.48 10.40 11.35 11.60 6.16 8.55 9.37 8.07 8.89 3.46
Fe2O3 - 8.93 11.95 - 13.24 9.79 10.80 11.88 6.87 11.20 11.87 12.32 7.98 9.80 10.79 9.98 10.53 3.95
MnO - 0.14 0.17 - 0.20 0.14 0.18 0.17 0.09 0.16 0.14 0.15 0.10 0.15 0.17 0.13 0.15 0.06
MgO - 3.82 9.99 - 7.10 3.02 2.99 4.35 2.93 2.70 2.91 2.32 10.35 6.40 5.04 12.06 5.43 3.26
CaO - 15.02 8.38 - 9.89 2.08 2.48 2.78 2.63 2.18 1.83 1.76 9.32 7.98 4.87 6.93 5.58 4.08
Na2O - 0.43 0.72 - 6.24 0.37 0.72 0.27 0.54 0.50 0.68 0.50 0.39 0.61 0.55 0.43 0.93 1.54
K2O - 0.97 0.91 - 1.27 3.13 2.38 1.25 2.40 4.16 3.51 2.51 0.97 0.88 2.67 2.47 2.11 1.07
P2O5 - 0.21 0.26 - 0.48 0.27 0.27 0.14 0.24 0.31 0.26 0.19 0.16 0.13 0.34 0.50 0.27 0.11
Cr2O3 - 0.09 0.17 - 0.01 0.10 0.13 0.11 0.07 0.14 0.13 0.12 0.08 0.13 0.12 0.13 0.11 0.04
NiO - 0.04 0.08 - 0.01 0.06 0.05 0.06 0.04 0.06 0.06 0.05 0.04 0.05 0.06 0.08 0.05 0.02
V2O5 - 0.04 0.05 - 0.06 0.04 0.05 0.05 0.03 0.05 0.05 0.05 0.06 0.04 0.05 0.05 0.05 0.01
ZrO2 - 0.04 0.04 - 0.03 0.07 0.05 0.04 0.04 0.07 0.08 0.06 0.03 0.02 0.05 0.05 0.05 0.02
CuO - 0.00 0.01 - 0.02 0.01 0.01 0.01 0.00 0.01 0.01 0.01 0.00 0.01 0.01 0.01 0.01 0.01
LOI - 17.12 9.81 - 2.59 25.96 8.83 12.21 38.97 6.91 7.41 8.79 18.90 9.48 9.54 5.96 13.03 9.57
Total 0.00 101.26 100.53 0.00 100.25 98.66 98.01 98.17 99.33 100.18 98.44 99.75 100.20 99.57 99.93 99.04 99.52 0.96
Y 30 23.00 24.00 25.00 27.00 37.00 28.00 26.00 35.00 35.00 39.00 31.00 18.00 24.00 42.00 50.00 30.88 8.29
Zr 369 255.00 310.00 301.00 258.00 581.00 309.00 299.00 488.00 510.00 565.00 389.00 211.00 203.00 437.00 477.00 372.63 123.38
ppm
As 0 0 0 0 0 0 0 0 0 1 0 0 0 3 2 5 0.69 1.45
Cu 97 61 94 91 72 105 81 84 80 89 94 96 60 66 87 93 84.38 13.45
Ga 18 11 14 13 13 19 13 15 18 18 20 18 10 14 18 23 15.94 3.57
Mo 2 1 2 2 1 5 2 2 3 5 5 2 0 10 15 16 4.56 4.88
Nb 22 13 15 12 12 31 21 15 22 31 25 19 11 12 25 25 19.44 6.80
Ni 393 265 547 590 382 565 356 434 431 474 508 383 278 338 464 280 418.00 102.32
Pb 8 3 1 1 2 14 4 4 11 15 13 5 1 4 12 12 6.88 5.14
Rb 48 24 24 20 29 74 47 37 54 73 65 57 27 21 50 51 43.81 18.31
Sr 242 182 260 322 185 472 229 128 511 439 529 239 713 225 398 774 365.50 192.98
Th 0 0 0 0 0 3 0 0 0 5 4 0 0 16 22 24 4.63 8.26
U 0 0 0 0 0 0 0 0 0 0 0 0 0 1 6 12 1.19 3.25
W* 41 21 20 6 52 15 44 20 55 60 28 35 23 329 286 101 71.00 95.42
Y 30 23 24 25 27 37 28 26 35 35 39 31 18 24 42 50 30.88 8.29
Zn 99 68 87 88 91 104 87 90 96 94 96 96 51 74 105 118 90.25 15.69
Zr 369 255 310 301 258 581 309 299 488 510 565 389 211 203 437 477 372.63 123.38
Table B2: Major and Trace Elements, XRF Results at Mooiplaas for the Reworked Residual Basalt Horizon.
AverageStandard
Deviation
Reworked Residual Basalt
Results indicated with a * should be considered semi-quantitative.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRF (wt % )
Test pit NB01 NB03 NB06 NB07 NB11 NB12 NB12 NB17 NB19 NB20 NB22 NB23 NB24 NB24 NB29 NB32 NB34
Depth (m) 0.4-0.5 0.25-0.50 0.48-.88 0.3-0.73 0.32-0.58 0.31-0.50 0.50-1.48 0.30-0.42 0.44-0.95 0.44-1.07 0.47-0.96 0.59-0.83 0.35-0.70 0.70-0.80 0.21-0.64 0.24-0.80 0.60-0.80
SiO2 - 49.61 - 70.51 - 71.55 38.16 22.20 35.14 39.92 44.81 44.98 55.65 48.38 36.40 46.35 42.85 46.18 13.16
TiO2 - 3.51 - 0.12 - 0.27 1.60 1.05 2.17 2.83 2.88 3.19 3.32 2.33 2.07 0.80 2.91 2.08 1.14
Al2O3 - 9.17 - 2.15 - 5.42 6.90 3.69 5.95 6.70 7.74 7.90 9.53 7.61 6.62 11.51 7.80 7.05 2.36
Fe2O3 - 12.01 - 0.70 - 1.63 9.55 4.59 9.04 8.20 8.47 9.48 9.85 9.51 8.00 10.46 9.64 7.94 3.30
MnO - 0.15 - 0.01 - 0.01 0.11 0.13 0.14 0.11 0.10 0.12 0.10 0.15 0.12 0.29 0.13 0.12 0.07
MgO - 9.77 - 0.03 - 0.35 7.63 2.47 7.16 7.63 5.66 9.04 7.04 4.79 5.27 2.94 7.62 5.53 3.07
CaO - 7.59 - 0.01 - 0.10 16.89 34.59 18.82 16.39 14.25 11.82 5.13 3.66 19.74 5.18 13.50 11.98 9.34
Na2O - 2.12 - 0.18 - 0.39 0.64 0.23 0.30 0.18 0.38 0.93 1.15 0.51 0.67 0.31 0.60 0.61 0.52
K2O - 1.52 - 0.99 - 2.71 1.05 0.62 0.60 3.10 4.00 2.68 3.16 1.66 1.31 0.48 1.65 1.82 1.11
P2O5 - 0.54 - 0.03 - 0.05 0.22 0.15 0.22 0.41 0.44 0.40 0.43 0.32 0.28 0.05 0.33 0.28 0.16
Cr2O3 - 0.11 - 0.00 - 0.00 0.08 0.05 0.09 0.09 0.10 0.12 0.11 0.10 0.07 0.09 0.12 0.08 0.04
NiO - 0.04 - 0.00 - 0.00 0.05 0.03 0.05 0.06 0.04 0.08 0.05 0.05 0.03 0.02 0.07 0.04 0.02
V2O5 - 0.06 - 0.00 - 0.01 0.03 0.02 0.03 0.04 0.04 0.05 0.05 0.04 0.03 0.03 0.05 0.03 0.02
ZrO2 - 0.06 - 0.05 - 0.03 0.02 0.02 0.03 0.06 0.06 0.07 0.07 0.03 0.04 0.02 0.04 0.04 0.02
CuO - 0.01 - 0.01 - 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.00 0.01 0.01 0.01 0.00
LOI - 4.12 - 25.20 - 18.16 17.22 30.84 19.93 14.84 12.10 9.55 3.79 20.53 18.55 20.29 11.93 16.22 7.53
Total 0.00 100.38 0.00 100.00 0.00 100.70 100.14 100.65 99.68 100.56 101.06 100.42 99.45 99.67 99.21 98.82 99.25 82.35 0.67
ppm
As 0 - 0 - 0 0 0 0 0 0 0 0 0 0 0 0 2 0.13 0.52
Cu 82 - 82 - 88 57 55 39 67 68 61 89 83 48 64 57 93 68.87 16.45
Ga 16 - 13 - 15 10 12 5 11 13 15 15 18 11 11 10 16 12.73 3.26
Mo 1 - 4 - 3 1 1 2 1 5 3 5 5 3 1 0 14 3.27 3.41
Nb 8 - 25 - 13 10 7 10 10 21 26 25 20 12 11 10 22 15.33 6.92
Ni 198 - 324 - 705 295 372 225 436 498 316 629 400 239 260 268 505 378.00 150.98
Pb 10 - 8 - 9 4 0 2 0 8 10 14 11 8 3 2 12 6.73 4.53
Rb 58 - 17 - 20 20 12 15 13 35 47 41 42 25 21 31 34 28.73 13.81
Sr 168 - 622 - 425 167 286 192 237 312 442 1078 960 566 488 1296 446 512.33 345.85
Th 1 - 1 - 0 0 0 0 0 1 1 1 1 0 0 0 25 2.07 6.36
U 0 - 0 - 0 0 0 0 0 0 0 5 3 0 0 1 9 1.20 2.60
W* 35 - 4 - 12 21 1 7 1 7 16 7 36 25 6 14 171 24.20 42.12
Y 20 - 22 - 23 20 17 26 22 25 27 32 36 21 26 21 32 24.67 5.29
Zn 63 - 76 - 100 66 78 35 76 77 74 88 90 54 66 51 95 72.60 17.47
Zr 210 - 316 - 296 187 137 129 209 406 419 546 553 304 298 269 393 311.47 131.70
AverageStandard
Deviation
Residual Basalt
Results indicated with a * should be considered semi-quantitative.
Table B3: Major and Trace Elements, XRF Results at Mooiplaas for the Residual Basalt Horizon.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRF (wt % )
Test pit NB01 NB12 NB15 NB19 NB34
Depth (m) 0.50-0.80 1.48-1.72 0.40-0.45 0.95 0.80-0.90
SiO2 49.20 32.96 49.80 35.68 41.74 41.88 7.65
TiO2 3.45 1.32 3.95 2.24 2.98 2.79 1.03
Al2O3 7.33 5.74 8.55 6.02 7.76 7.08 1.19
Fe2O3 10.42 8.37 10.25 9.41 9.39 9.57 0.82
MnO 0.13 0.10 0.14 0.13 0.12 0.12 0.02
MgO 14.04 7.12 8.53 8.11 8.39 9.24 2.74
CaO 6.14 21.92 6.06 18.23 15.06 13.48 7.16
Na2O 1.71 0.65 0.37 0.40 0.84 0.80 0.55
K2O 2.75 0.78 5.40 0.58 1.58 2.22 1.98
P2O5 0.47 0.19 0.64 0.24 0.35 0.38 0.18
Cr2O3 0.12 0.07 0.13 0.11 0.11 0.11 0.03
NiO 0.08 0.04 0.06 0.06 0.07 0.06 0.02
V2O5 0.05 0.02 0.06 0.04 0.05 0.04 0.01
ZrO2 0.08 0.02 0.10 0.03 0.04 0.05 0.03
CuO 0.01 0.00 0.01 0.01 0.01 0.01 0.00
LOI 3.38 20.39 4.76 18.52 11.16 11.64 7.74
Total 99.39 99.69 98.82 99.80 99.64 99.47 0.39
ppm
As 0 0 4 0 0 0.80 1.79
Cu 84 44 94 67 88 75.40 20.22
Ga 15 10 21 11 15 14.40 4.34
Mo 0 1 8 2 16 5.40 6.69
Nb 5 7 44 8 20 16.80 16.30
Ni 160 329 516 453 476 386.80 144.75
Pb 8 0 21 0 8 7.40 8.59
Rb 52 9 78 10 32 36.20 29.33
Sr 167 294 992 267 561 456.20 333.09
Th 0 0 12 0 23 7.00 10.34
U 0 0 9 0 11 4.00 5.52
W* 76 1 20 1 75 34.60 38.14
Y 18 14 36 20 35 24.60 10.19
Zn 68 67 104 77 96 82.40 16.77
Zr 136 113 744 213 392 319.60 261.30
Results indicated with a * should be considered semi-quantitative.
AverageStandard
Deviation
Highly Weathered Basalt
Table B4: Major and Trace Elements, XRF Results at Mooiplaas for the Highly Weathered Basalt.
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRF (wt % )
Test pit NB14 NB17 NB29 NB27 Outcrop 4 Outcrop 5
Depth (m) Surface Surface Surface 1.00-1.50 Surface Surface
SiO2 39.15 48.55 51.00 50.43 44.95 45.77 46.64 4.40 51.00 39.15
TiO2 2.66 3.10 3.55 3.59 2.40 2.42 2.95 0.54 3.59 2.40
Al2O3 12.89 8.43 9.79 11.77 11.65 10.59 10.86 1.59 12.89 8.43
Fe2O3 12.08 12.79 11.99 11.07 12.73 13.07 12.29 0.73 13.07 11.07
MnO 0.22 0.17 0.15 0.14 0.19 0.21 0.18 0.03 0.22 0.14
MgO 5.70 15.01 10.50 5.04 6.83 7.22 8.38 3.76 15.01 5.04
CaO 9.72 7.74 7.76 7.72 9.43 10.46 8.81 1.21 10.46 7.72
Na2O 7.25 1.39 1.86 1.30 6.54 4.50 3.81 2.67 7.25 1.30
K2O 0.90 1.39 1.59 3.03 1.43 1.02 1.56 0.77 3.03 0.90
P2O5 1.10 0.38 0.54 0.44 0.39 0.38 0.54 0.28 1.10 0.38
Cr2O3 0.01 0.15 0.12 0.06 0.01 0.01 0.06 0.06 0.15 0.01
NiO 0.02 0.10 0.06 0.05 0.02 0.02 0.04 0.03 0.10 0.02
V2O5 0.06 0.05 0.06 0.06 0.06 0.06 0.06 0.00 0.06 0.05
ZrO2 0.03 0.04 0.05 0.05 0.02 0.02 0.03 0.02 0.05 0.02
CuO 0.04 0.01 0.01 0.01 0.03 0.03 0.02 0.01 0.04 0.01
LOI 8.02 0.35 0.55 4.48 2.57 3.53 3.25 2.85 8.02 0.35
TOTAL 99.84 99.66 99.59 99.24 99.26 99.31 99.49 0.25 99.84 99.24
ppm
As 4 0 5 0 0 0 1.50 2.35 5.00 0.00
Cu 289 108 107 82 218 216 170.00 82.63 289.00 82.00
Ga 27 19 21 16 16 11 18.33 5.43 27.00 11.00
Mo 11 15 16 14 11 11 13.00 2.28 16.00 11.00
Nb 100 23 18 19 70 69 49.83 34.57 100.00 18.00
Ni 26 726 364 555 51 82 300.67 295.02 726.00 26.00
Pb 19 8 8 6 12 15 11.33 4.97 19.00 6.00
Rb 30 29 40 43 43 34 36.50 6.35 43.00 29.00
Sr 1453 929 1238 501 1162 998 1046.83 325.26 1453.00 501.00
Th 26 30 25 21 22 28 25.33 3.44 30.00 21.00
U 16 10 15 7 9 9 11.00 3.63 16.00 7.00
W* 80 178 263 35 124 78 126.33 82.68 263.00 35.00
Y 29 35 38 34 19 20 29.17 8.04 38.00 19.00
Zn 132 118 121 106 123 126 121.00 8.76 132.00 106.00
Zr 278 386 462 465 213 213 336.17 117.17 465.00 213.00
Table B5: Major and Trace Elements, XRF Results at Mooiplaas for Basalt Rock Samples.
Results indicated with a * should be considered semi-quantitative.
Rock Samples
AverageStandard
DeviationMaximum Minimum
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRF
(wt% )
Test pit SB02 SB17 SB02 SB16 SB17 SB29 SB16 SB23 SB10A SB10J
Depth (m) 0.00-0.12 0.00-0.64 0.12-0.55 0.38-0.65 0.64-0.84 0.81-1.3 0.65-1.03 0.12-0.40 Surface Surface
SiO2 57.76 49.22 53.49 6.04 47.55 56.20 39.46 50.02 48.31 6.93 53.15 50.21 51.68 2.08 49.99 51.79 50.89 1.27
TiO2 3.34 3.63 3.49 0.21 3.02 3.47 2.56 3.17 3.06 0.38 3.27 2.44 2.86 0.58 3.29 1.13 2.21 1.53
Al2O3 11.32 11.82 11.57 0.35 13.49 11.85 11.54 11.62 12.13 0.92 12.98 13.24 13.11 0.18 14.58 14.62 14.60 0.03
Fe2O3 14.48 22.26 18.37 5.51 18.74 13.79 16.18 16.11 16.21 2.02 13.00 15.28 14.14 1.62 12.46 12.41 12.43 0.04
MnO 0.19 0.23 0.21 0.03 0.43 0.14 0.28 0.24 0.27 0.12 0.18 0.22 0.20 0.03 0.12 0.20 0.16 0.05
MgO 1.14 1.03 1.09 0.08 4.06 1.10 1.76 2.46 2.34 1.27 2.39 5.45 3.92 2.17 3.89 6.55 5.22 1.88
CaO 0.85 0.74 0.80 0.07 1.79 1.22 10.72 6.29 5.01 4.44 3.74 9.71 6.72 4.22 6.91 8.50 7.71 1.12
Na2O 0.41 0.73 0.57 0.23 0.40 0.98 0.67 1.56 0.90 0.50 1.73 1.98 1.85 0.17 3.52 3.12 3.32 0.28
K2O 1.53 1.48 1.51 0.03 1.62 2.00 1.31 1.70 1.66 0.29 2.52 0.86 1.69 1.18 2.98 1.35 2.16 1.15
P2O5 0.16 0.26 0.21 0.07 0.20 0.27 0.14 1.28 0.47 0.54 0.47 0.30 0.38 0.12 0.66 0.13 0.40 0.37
Cr2O3 0.08 0.06 0.07 0.02 0.13 0.03 0.03 0.01 0.05 0.05 0.01 0.01 0.01 0.00 0.01 0.03 0.02 0.01
NiO 0.02 <0.01 0.02 0.01 0.06 <0.01 <0.01 <0.01 0.06 0.03 <0.01 <0.01 <0.01 0.00 <0.01 <0.01 <0.01 0.00
V2O5 0.06 0.08 0.07 0.02 0.06 0.06 0.06 0.04 0.05 0.01 0.06 0.08 0.07 0.01 0.05 0.05 0.05 0.00
ZrO2 0.05 0.04 0.04 0.01 0.03 0.05 0.03 0.04 0.04 0.01 0.04 0.02 0.03 0.01 0.05 0.01 0.03 0.03
CuO <0.01 <0.01 <0.01 0.00 <0.01 <0.01 <0.01 <0.01 <0.01 0.00 <0.01 <0.01 <0.01 0.00 <0.01 <0.01 <0.01 0.00
LOI 9.21 9.59 9.40 0.27 9.40 9.15 15.82 5.72 10.02 4.22 7.19 1.18 4.19 4.25 2.76 1.97 2.36 0.56
TOTAL 100.57 101.18 100.88 0.43 101.00 100.31 100.55 100.25 100.53 0.34 100.73 100.97 100.85 0.17 101.27 101.85 101.56 0.42
Standard
DeviationAverage
Standard
DeviationAverage
Standard
DeviationAverage
Standard
DeviationAverage
Table B6a: Major Elements, XRF Results at Nhlowa.
Colluvium Residual Basalt Highly Weathered Basalt Rock Samples
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRF (ppm)
Test pit SB02 SB17 SB02 SB16 SB17 SB29 SB16 SB23 SB10A SB10J
Depth (m) 0.00-0.12 0.00-0.64 0.12-0.55 0.38-0.65 0.64-0.84 0.81-1.3 0.65-1.03 0.12-0.40 Surface Surface
As 22.97 25.91 24.44 2.08 31.05 28.15 23.42 21.15 25.94 4.48 16.62 26.62 21.62 7.07 22.98 18.50 20.74 3.17
Cu 136.14 225.76 180.95 63.37 144.39 131.86 189.27 195.68 165.30 31.90 97.24 224.15 160.69 89.74 136.56 133.64 135.10 2.06
Ga 22.47 22.33 22.40 0.10 27.91 21.46 22.73 24.38 24.12 2.80 21.78 23.83 22.80 1.45 27.85 20.82 24.33 4.98
Mo 2.16 4.90 3.53 1.94 3.85 1.30 3.81 4.03 3.25 1.30 7.57 3.90 5.74 2.59 3.71 2.03 2.87 1.19
Nb 21.25 27.43 24.34 4.37 20.40 23.31 19.87 31.95 23.88 5.58 25.80 17.53 21.66 5.85 31.44 8.02 19.73 16.56
Ni 191.47 100.18 145.83 64.55 579.00 74.92 89.17 57.12 200.05 252.97 68.49 54.44 61.47 9.93 61.44 72.33 66.89 7.70
Pb 10.29 8.91 9.60 0.98 17.83 16.49 5.36 8.70 12.09 6.03 12.54 4.75 8.64 5.51 11.78 9.00 10.39 1.97
Rb 50.56 56.72 53.64 4.36 49.30 51.83 46.38 45.38 48.22 2.93 53.00 22.18 37.59 21.79 68.89 50.39 59.64 13.08
Sr 141.64 137.40 139.52 3.00 225.13 350.92 174.59 414.66 291.33 110.71 505.61 301.60 403.60 144.26 902.17 460.98 681.57 311.97
Th 4.58 11.84 8.21 5.13 8.32 6.96 7.93 14.01 9.31 3.19 9.53 11.38 10.46 1.30 12.56 7.42 9.99 3.63
U 3.00 9.77 6.39 4.79 6.62 3.00 7.21 8.45 6.32 2.34 7.43 9.27 8.35 1.30 13.37 5.17 9.27 5.80
W* 229.33 101.20 165.26 90.60 6.00 94.56 6.00 90.08 49.16 49.87 6.00 6.00 6.00 0.00 6.00 91.15 48.58 60.21
Y 30.62 47.79 39.20 12.14 26.17 32.64 58.43 59.92 44.29 17.40 48.54 51.61 50.08 2.17 46.07 26.06 36.07 14.15
Zn 89.05 100.81 94.93 8.32 94.81 103.06 94.78 130.53 105.80 16.94 110.40 104.53 107.46 4.15 130.08 95.14 112.61 24.71
Zr 383.92 365.08 374.50 13.32 337.61 386.08 267.73 371.63 340.76 52.76 374.67 240.94 307.81 94.56 474.66 89.79 282.23 272.15
Cl* 7.58 7.58 7.58 0.00 7.58 7.58 7.58 7.58 7.58 0.00 7.58 7.58 7.58 0.00 7.58 7.58 7.58 0.00
Co 118.64 82.03 100.33 25.88 142.29 67.44 57.72 64.71 83.04 39.71 45.91 42.71 44.31 2.26 33.09 57.70 45.39 17.40
Cr 613.66 451.13 532.40 114.92 990.10 194.81 227.88 73.63 371.61 417.63 84.38 71.71 78.05 8.96 69.64 181.60 125.62 79.17
F* 100.00 100.00 100.00 0.00 100.00 100.00 100.00 100.00 100.00 0.00 100.00 100.00 100.00 0.00 100.00 100.00 100.00 0.00
S* 16.00 55.18 35.59 27.70 16.55 16.00 52.54 16.00 25.27 18.18 16.00 16.00 16.00 0.00 16.00 16.00 16.00 0.00
Sc 29.17 35.22 32.20 4.27 29.31 26.25 32.66 29.84 29.51 2.63 24.04 37.63 30.84 9.61 16.36 31.23 23.80 10.51
V 328.26 532.50 430.38 144.42 356.82 344.54 412.98 215.32 332.42 83.55 376.72 387.70 382.21 7.76 258.26 258.91 258.59 0.46
Cs 14.22 16.29 15.26 1.46 14.05 21.75 28.74 24.87 22.35 6.23 19.04 26.25 22.64 5.10 35.83 33.78 34.81 1.45
Ba 557.04 674.82 615.93 83.28 878.87 856.84 745.00 890.16 842.72 66.60 1460.58 531.71 996.14 656.81 1271.40 270.12 770.76 708.01
La 4.26 4.53 4.39 0.19 21.34 5.90 34.70 30.79 23.18 12.81 34.36 4.26 19.31 21.28 33.67 4.35 19.01 20.74
Ce 105.59 107.23 106.41 1.16 303.92 127.64 133.30 152.81 179.42 83.70 187.53 69.19 128.36 83.68 186.58 24.94 105.76 114.29
Standard
Deviation
Results indicated with a * should be considered semi-quantitative.
Table B6b: Trace Elements, XRF Results at Nhlowa.
Colluvium Residual Basalt Highly Weathered Basalt Rock Samples
AverageStandard
DeviationAverage
Standard
DeviationAverage
Standard
DeviationAverage
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRF
(wt% )
Reworked
Pebble
Marker/
Residuum
Test pit TP01 TP03 TP05 TP01 TP01 TP03 TP05 TP05 TP08 TP08 TP08
Depth (m) 0.0-0.7 0.0-1.0 0.0-0.6 1.0-1.4 1.5-2.5 1.5-2.0 0.8-1.2 1.7 0.7-1.1 2.0-2.5 2.5-3.0
SiO2 45.85 49.73 48.59 48.06 2.00 69.98 51.37 51.12 41.65 48.08 48.18 49.02 47.65 48.15 3.23
TiO2 2.18 1.82 1.87 1.95 0.19 0.60 1.63 1.53 1.69 1.69 1.69 1.38 1.49 1.59 0.12
Al2O3 6.76 16.24 16.86 13.29 5.66 7.80 15.05 14.12 15.53 14.78 14.17 14.50 15.45 14.80 0.57
Fe2O3 8.37 15.50 16.00 13.29 4.27 15.04 14.54 14.35 17.18 14.13 13.79 12.88 14.26 14.45 1.32
MnO 0.12 0.24 0.19 0.18 0.06 0.48 0.20 0.31 0.44 0.21 0.21 0.18 0.24 0.26 0.09
MgO 13.13 1.08 0.91 5.04 7.01 0.31 2.75 2.14 2.15 5.82 1.38 5.08 5.93 3.61 1.93
CaO 11.54 4.04 3.39 6.32 4.53 0.41 6.16 6.20 8.91 10.05 6.63 3.30 3.22 6.35 2.56
Na2O 1.07 0.65 0.48 0.73 0.31 0.26 1.46 0.71 0.66 1.82 0.71 2.53 3.45 1.62 1.06
K2O 1.19 0.42 0.32 0.65 0.48 0.20 0.16 0.29 0.23 0.44 0.41 0.81 0.92 0.46 0.29
P2O5 0.12 0.07 0.08 0.09 0.03 0.07 0.08 0.06 0.07 0.18 0.06 0.11 0.14 0.10 0.05
Cr2O3 0.08 0.03 0.03 0.05 0.03 0.03 0.02 0.02 0.03 0.03 0.03 0.02 0.02 0.02 0.00
NiO 0.04 0.01 0.01 0.02 0.02 0.01 0.01 0.02 0.02 0.03 0.01 0.01 0.02 0.02 0.00
V2O5 0.08 0.06 0.06 0.07 0.01 0.04 0.05 0.05 0.06 0.05 0.06 0.04 0.05 0.05 0.00
ZrO2 0.04 0.03 0.03 0.03 0.01 0.01 0.02 0.02 0.02 0.02 0.03 0.02 0.02 0.02 0.00
CuO 0.00 0.02 0.02 0.01 0.01 0.01 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.00
LOI 9.36 10.08 11.14 10.20 0.90 4.69 7.15 8.70 12.21 2.84 11.64 10.23 6.60 8.48 3.27
TOTAL 99.95 100.01 99.99 99.98 0.03 99.94 100.69 99.66 100.87 100.20 99.01 100.14 99.48 100.01 0.67
Table B7a: Major Elements, XRF Results for the Sibasa Basalt at Siloam.
Colluvium Residual Basalt
AverageStandard
DeviationAverage
Standard
Deviation
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRF (ppm)
Reworked
Pebble
Marker/
Residuum
Test pit TP01 TP03 TP05 TP01 TP01 TP03 TP05 TP05 TP08 TP08 TP08
Depth (m) 0.0-0.7 0.0-1.0 0.0-0.6 1.0-1.4 1.5-2.5 1.5-2.0 0.8-1.2 1.7 0.7-1.1 2.0-2.5 2.5-3.0
As 0 0 0 0.00 0.00 0 0 0 0 0 0 0 0 0.00 0.00
Cu 177 207 197 193.67 15.28 164 256 210 244 233 169 196 184 213.14 32.36
Ga 21 22 22 21.67 0.58 15 21 20 20 20 19 16 18 19.14 1.68
Mo 2 3 3 2.67 0.58 2 2 2 1 1 3 0 0 1.29 1.11
Nb 10 11 10 10.33 0.58 4 10 10 9 10 9 6 7 8.71 1.60
Ni 103 119 113 111.67 8.08 120 133 159 168 138 99 119 136 136.00 23.18
Pb 12 11 11 11.33 0.58 14 6 10 5 1 8 2 0 4.57 3.74
Rb 47 34 29 36.67 9.29 16 9 20 16 13 30 25 24 19.57 7.37
Sr 128 127 129 128.00 1.00 24 227 160 216 271 123 100 79 168.00 71.91
Th 2 0 0 0.67 1.15 0 0 1 0 0 0 0 0 0.14 0.38
U 0 0 0 0.00 0.00 0 0 0 0 0 0 0 0 0.00 0.00
W* 70 17 182 89.67 84.24 89 21 44 25 48 20 13 2 24.71 16.35
Y 32 37 35 34.67 2.52 8 34 30 32 29 32 23 27 29.57 3.69
Zn 91 74 68 77.67 11.93 26 91 74 75 118 58 93 101 87.14 19.84
Zr 199 195 195 196.33 2.31 68 155 153 167 156 184 115 119 149.86 24.84
Results indicated with a * should be considered semi-quantitative.
Table B7b: Trace Elements, XRF Results for the Sibasa Basalt at Siloam.
Colluvium Residual Basalt
AverageStandard
DeviationAverage
Standard
Deviation
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRF (wt % )
Highly
Weathered
Basalt
Slightly
Weathered
Basalt
Test pit S01 S01 S01 SR
Depth (m) 0.00-0.30 0.30-1.00 1.00-2.00 Surface
SiO2 46.40 52.94 47.00 50.52
TiO2 2.49 0.86 0.93 0.97
Al2O3 11.50 13.22 14.33 14.85
Fe2O3 14.80 9.07 10.70 11.09
MnO 0.23 0.16 0.16 0.16
MgO 5.09 3.13 5.84 6.21
CaO 8.32 6.51 10.08 9.86
Na2O 1.97 1.11 1.91 2.12
K2O 0.62 0.61 0.51 0.46
P2O5 0.27 0.10 0.15 0.16
Cr2O3 0.01 0.03 0.03 0.03
NiO 0.01 0.01 0.01 0.01
V2O5 0.06 0.03 0.04 0.04
ZrO2 0.02 0.02 0.01 0.01
CuO 0.02 0.01 0.01 0.01
LOI 9.19 10.59 6.92 2.81
TOTAL 101.01 98.39 98.62 99.31
ppm
As 0 0 0.00 0.00
Cu 76 85 90.00 96.00
Ga 14 15 19.00 18.00
Mo 2 1 0.00 2.00
Nb 10 9 8.00 8.00
Ni 61 63 67.00 71.00
Pb 9 8 6.00 6.00
Rb 47 30 9.00 11.00
Sr 54 129 240.00 241.00
Th 0 0 0.00 0.00
U 0 0 0.00 0.00
W* 28 19 21.00 32.00
Y 26 24 21.00 23.00
Zn 71 74 85.00 84.00
Zr 202 146 107.00 105.00
Results indicated with a * should be considered semi-quantitative.
Residual Basalt
Table B8: Major and Trace Elements, XRF Results for the Springbok Flats Basalt at Codrington
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
Appendix C
XRD Results
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRD (wt % )
Sample nr NB01 NB03 NB30 NB30 NB31 NB32
Depth (m) 0.00-0.40 0.00-0.25 0.00-0.38 0.38-0.61 0.00-0.90 0.00-0.24
Augite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Diopside 9.93 8.22 9.08 1.21 6.39 8.06 7.76 0.00 5.55 3.77
Chlorite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Muscovite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Enstatite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Goethite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Kaolinite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Ilmenite 0.00 0.00 0.00 0.00 2.23 2.32 1.64 1.50 1.92 0.41
Magnetite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Hematite 6.12 0.00 3.06 4.33 0.00 0.00 0.00 0.00 0.00 0.00
Hornblende 0.00 3.85 1.93 2.72 0.00 0.00 0.00 0.00 0.00 0.00
Forsterite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Microcline 10.06 0.00 5.03 7.11 0.00 0.00 0.00 0.00 0.00 0.00
Orthoclase 0.00 0.00 0.00 0.00 6.14 6.75 0.00 0.00 3.22 3.73
Plagioclase 23.00 23.66 23.33 0.47 0.00 0.00 0.00 0.00 0.00 0.00
Quartz 50.88 14.59 32.74 25.66 16.10 14.93 7.28 24.29 15.65 6.96
Smectite 0.00 49.68 24.84 35.13 0.00 0.00 0.00 0.00 0.00 0.00
Titanite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Calcite,
magnesian0.00 0.00 0.00 0.00 6.63 13.98 3.56 4.07 7.06 4.80
Talc 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Rutile 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Palygorskite 0.00 0.00 0.00 0.00 62.50 53.95 79.76 45.88 60.52 14.51
Dolomite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 24.26 6.07 12.13
Anatase 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Analcime 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Actinolite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Natrolite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Nepheline 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Laumonite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Total 99.99 100.00 100.00 0.01 99.99 99.99 100.00 100.00 100.00 0.01
0.00
Average and Standard deviation calculations include samples with zero values
Zero Values are greyed out to accentuate quantitative values
Table C1: XRD Results for Colluvium and Alluvium Horizons of the Mooiplaas Site
Colluvium Alluvium
Standard
DeviationAverage
Standard
DeviationAverage
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRD (wt % )
Sample nr NB06 NB07 NB11 NB11 NB12 NB15 NB17 NB19 NB20 NB22 NB24 NB29 NB31 NB33 NB34 NB34
Depth (m) 0.00-0.48 0.00-0.30 0.00-0.24 0.24-0.32 0.00-0.31 0.00-0.40 0.00-0.30 0.00-0.44 0.00-0.44 0.00-0.47 0.00-0.35 0.00-0.21 0.90-1.20 0.00-0.25 0.00-0.30 0.30-0.60
Augite 0.00 0.00 14.71 0.00 5.98 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 30.55 37.50 5.55 11.83
Diopside 4.83 2.58 0.00 18.74 0.00 8.03 4.97 2.47 16.43 6.69 3.98 1.16 6.11 14.12 0.00 0.00 5.63 5.99
Chlorite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Muscovite 0.00 0.00 0.00 4.50 1.71 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.39 1.18
Enstatite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 6.96 0.00 20.57 0.00 0.00 1.72 5.32
Goethite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Kaolinite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Ilmenite 0.00 0.00 2.15 1.90 2.11 0.00 2.64 3.31 4.02 4.51 4.70 2.98 0.00 0.00 4.78 1.68 2.17 1.79
Magnetite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Hematite 1.93 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.12 0.48
Hornblende 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.74 0.00 0.30 1.19
Forsterite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Microcline 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Orthoclase 0.00 0.00 0.00 0.00 0.00 17.08 0.00 0.00 0.00 18.13 16.24 6.97 5.45 0.00 19.24 15.09 6.14 7.99
Plagioclase 14.22 6.43 9.44 11.71 9.09 4.72 7.49 7.03 12.06 0.00 0.00 0.00 0.00 21.34 12.63 30.66 9.18 8.30
Quartz 16.51 14.43 7.14 5.84 20.93 9.23 18.98 12.19 19.37 19.89 15.00 19.97 12.01 30.39 23.37 8.46 15.86 6.61
Smectite 62.50 38.83 55.31 47.67 60.17 60.94 65.92 49.20 48.12 50.77 60.09 61.95 0.00 0.00 0.00 0.00 41.34 25.61
Titanite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Calcite,
magnesian0.00 27.64 0.00 0.00 0.00 0.00 0.00 2.08 0.00 0.00 0.00 0.00 2.10 13.58 4.68 6.58 3.54 7.40
Talc 0.00 0.00 0.00 2.70 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.17 0.68
Rutile 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Palygorskite 0.00 10.09 11.25 6.94 0.00 0.00 0.00 23.71 0.00 0.00 0.00 0.00 53.55 0.00 0.00 0.00 6.60 14.17
Dolomite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 20.77 0.00 0.00 0.00 1.30 5.19
Anatase 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Analcime 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Actinolite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Natrolite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Nepheline 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Laumonite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Total 99.99 100.00 100.00 100.00 99.99 100.00 100.00 99.99 100.00 99.99 100.01 99.99 99.99 100.00 99.99 99.97 99.99 0.01
0.00 Zero Values are greyed out to accentuate quantitative values
Average and Standard deviation calculations include samples with zero values
Table C2: XRD Results for Reworked Residual Basalt Horizon of the Mooiplaas Site.
Standard
DeviationAverage
Reworked Residual Basalt
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRD (wt % )
Sample nr NB01 NB03 NB06 NB07 NB11 NB12 NB12 NB17 NB19 NB20 NB22 NB23 NB24 NB24 NB29 NB34
Depth (m) 0.40-0.50 0.25-0.50 0.48-0.88 0.30-0.73 0.32-0.58 0.31-0.50 0.50-1.48 0.30-0.42 0.44-0.95 0.44-1.07 0.47-0.96 0.59-0.87 0.35-0.70 0.70-0.80 0.21-0.64 0.60-0.80
Augite 0.00 0.00 0.00 0.00 0.00 3.65 7.84 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 20.07 1.97 5.26
Diopside 6.16 21.53 12.82 3.86 24.20 0.00 0.00 0.00 5.09 11.08 13.29 16.83 17.78 6.89 11.14 0.00 9.42 7.93
Chlorite 0.00 0.00 25.67 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.60 6.42
Muscovite 0.00 4.77 0.00 1.82 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.41 1.25
Enstatite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Goethite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Kaolinite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Ilmenite 0.00 0.00 0.00 0.00 2.54 0.97 0.00 1.21 2.81 2.57 3.61 2.36 5.26 2.13 2.43 3.30 1.82 1.59
Magnetite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Hematite 2.97 0.00 0.00 0.00 0.00 0.00 0.44 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.21 0.74
Hornblende 3.94 3.46 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.46 1.27
Forsterite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Microcline 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Orthoclase 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 8.75 20.59 14.36 20.08 9.20 0.00 10.60 5.22 7.62
Plagioclase 23.18 31.46 19.14 2.40 18.91 6.92 9.73 0.00 5.13 0.00 0.00 0.00 0.00 0.00 5.89 10.00 8.30 9.86
Quartz 20.86 6.00 1.34 8.79 0.71 10.54 3.77 7.39 2.51 4.65 4.92 2.46 11.04 7.47 4.71 0.00 6.07 5.16
Smectite 42.89 22.11 41.03 25.72 44.20 39.07 50.32 0.00 57.47 47.00 36.25 40.96 45.84 22.05 37.60 34.67 36.70 13.77
Titanite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Calcite,
magnesian0.00 10.68 0.00 0.00 9.44 32.20 27.90 90.17 0.00 25.93 21.34 16.65 0.00 52.26 38.22 21.37 21.64 24.10
Talc 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 6.38 0.00 0.00 0.00 0.00 0.40 1.60
Rutile 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.23 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.08 0.31
Palygorskite 0.00 0.00 0.00 57.41 0.00 6.65 0.00 0.00 26.99 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5.69 15.38
Dolomite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Anatase 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Analcime 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Actinolite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Natrolite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Nepheline 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Laumonite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Total 100.00 100.01 100.00 100.00 100.00 100.00 100.00 100.00 100.00 99.98 100.00 100.00 100.00 100.00 99.99 100.01 100.00 0.01
0.00
Average and Standard deviation calculations include samples with zero values
Zero Values are greyed out to accentuate quantitative values
Table C3: XRD Results for Residual Basalt Horizon of the Mooiplaas Site.
Standard
DeviationAverage
Residual Basalt
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRD (wt % )
Sample nr NB01 NB12 NB15 NB19 NB34-4 NB14 NB17 NB29 NB27
Depth (m) 0.50-0.80 1.48-1.72 0.40-0.45 0.95 0.80-0.90 Surface Surface Surface 0.40-0.60
Augite 0.00 8.22 0.00 0.00 26.71 6.99 11.59 26.49 44.16 47.83 26.34 46.57 61.51 42.15 13.61
Diopside 16.98 0.00 28.55 6.29 0.00 10.36 12.31 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Chlorite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Muscovite 3.75 0.00 1.78 0.00 0.00 1.11 1.67 0.00 0.00 0.00 0.00 1.42 4.15 0.93 1.68
Enstatite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Goethite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Kaolinite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Ilmenite 0.00 0.60 3.88 2.47 2.83 1.96 1.61 0.00 3.03 4.52 0.00 0.00 0.00 1.26 2.01
Magnetite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 9.07 0.00 0.00 0.00 5.48 5.84 3.40 3.93
Hematite 3.48 0.18 0.00 0.00 0.00 0.73 1.54 0.00 0.00 0.00 0.00 1.62 2.12 0.62 0.98
Hornblende 2.79 0.00 0.87 0.00 0.00 0.73 1.21 0.00 0.00 0.00 0.00 7.22 0.00 1.20 2.95
Forsterite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 22.96 10.45 0.00 0.00 0.00 5.57 9.49
Microcline 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Orthoclase 0.00 0.00 0.00 0.00 9.76 1.95 4.36 0.00 0.00 0.00 9.52 0.00 0.00 1.59 3.89
Plagioclase 32.88 9.74 22.92 8.49 12.09 17.22 10.44 0.00 29.86 37.20 0.00 0.00 0.00 11.18 17.47
Quartz 14.26 2.93 2.57 2.41 0.00 4.43 5.61 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Smectite 25.85 40.87 39.44 52.43 25.86 36.89 11.26 0.00 0.00 0.00 56.29 0.00 0.00 9.38 22.98
Titanite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Calcite,
magnesian0.00 37.46 0.00 27.90 22.75 17.62 16.93 4.94 0.00 0.00 0.00 0.00 0.00 0.82 2.02
Talc 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Rutile 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Palygorskite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Dolomite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Anatase 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Analcime 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.35 11.53 11.98 4.48 5.79
Actinolite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 9.22 0.00 0.00 0.00 0.00 0.00 1.54 3.76
Natrolite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 50.28 0.00 0.00 0.00 12.25 14.40 12.82 19.49
Nepheline 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 13.92 0.00 2.32 5.68
Laumonite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.50 0.00 0.00 0.75 1.84
Total 99.99 100.00 100.01 99.99 100.01 100.00 0.01 100.00 100.01 100.00 100.00 100.01 100.00 100.00 0.01
0.00
Average and Standard deviation calculations include samples with zero values
Zero Values are greyed out to accentuate quantitative values
Table C4: XRD Results for Highly Weathered Basalt Horizon and Rocks of the Mooiplaas Site.
Highly weathered Basalt Rock samples
Outcrop 4 Outcrop 5AverageStandard
Deviation
Standard
DeviationAverage
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRD (wt % )
Sample nr SB02 SB17 SB02 SB16 SB17 SB29 SB16 SB23 SB10A SB10J
Depth (m) 0.00-0.12 0.00-0.64 0.12-0.55 0.38-0.65 0.64-0.84 1.30 0.65-1.03 0.12-0.40 Surface Surface
Augite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Diopside 3.60 4.43 4.02 0.59 4.75 0.00 0.00 0.00 1.19 2.38 2.19 33.72 17.96 22.30 0.00 31.30 15.65 22.13
Chlorite 0.00 0.00 0.00 0.00 3.56 0.00 0.00 0.00 0.89 1.78 0.00 3.91 1.96 2.76 22.80 18.21 20.51 3.25
Muscovite 0.00 0.00 0.00 0.00 0.00 0.00 16.07 11.04 6.78 8.09 0.00 0.00 0.00 0.00 0.00 8.14 4.07 5.76
Enstatite 0.00 0.00 0.00 0.00 0.00 5.90 0.00 0.00 1.48 2.95 0.00 0.00 0.00 0.00 0.00 4.18 2.09 2.96
Goethite 0.00 48.04 24.02 33.97 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Kaolinite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Ilmenite 8.88 4.65 6.77 2.99 6.55 6.10 5.01 5.02 5.67 0.78 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Magnetite 0.00 0.00 0.00 0.00 0.00 0.00 3.18 0.00 0.80 1.59 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Hematite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.42 0.00 0.71 1.00
Hornblende 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4.46 2.23 3.15
Forsterite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Microcline 9.37 4.44 6.91 3.49 8.23 0.00 8.00 5.59 5.46 3.83 8.39 0.00 4.20 5.93 31.92 0.00 15.96 22.57
Orthoclase 0.00 0.00 0.00 0.00 0.00 18.36 0.00 0.00 4.59 9.18 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Plagioclase 14.98 5.60 10.29 6.63 10.90 18.50 7.11 14.99 12.88 4.94 19.45 58.03 38.74 27.28 28.73 33.70 31.22 3.51
Quartz 63.17 32.84 48.01 21.45 66.01 51.14 22.44 45.14 46.18 18.10 10.63 4.34 7.49 4.45 4.31 0.00 2.16 3.05
Smectite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 18.22 4.56 9.11 59.34 0.00 29.67 41.96 0.00 0.00 0.00 0.00
Titanite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 10.83 0.00 5.42 7.66
Calcite,
magnesian0.00 0.00 0.00 0.00 0.00 0.00 38.19 0.00 9.55 19.10 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Total 100.00 100.00 100.00 0.00 100.00 100.00 100.00 100.00 100.00 0.00 100.00 100.00 100.00 0.00 100.01 99.99 100.00 0.01
0.00
Average and Standard deviation calculations include samples with zero values
Zero Values are greyed out to accentuate quantitative values
Table C5: XRD results for the Nhlowa site.
Rock Sample
AverageStandard
Deviation
Colluvium Residual Basalt Highly Weathered Basalt
AverageStandard
DeviationAverage
Standard
DeviationAverage
Standard
Deviation
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRD (wt % )
Reworked
Pebble
Marker/
Residuum
Sample nr TP01 TP03 TP05 TP01 TP01 TP03 TP05 TP05 TP08 TP08 TP08
Depth (m) 0.0-0.7 0.0-1.0 0.0-0.6 1.0-1.4 1.5-2.5 1.5-2.0 0.8-1.0 1.7 0.7-1.1 2.0-2.5 2.5-3.0
Augite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.51 4.01 0.79 1.53
Actinolite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3.25 0.00 0.00 5.05 1.19 2.09
Diopside 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 21.63 0.00 0.00 0.00 3.09 8.18
Epidote 10.91 10.28 17.18 12.79 3.81 0.00 18.89 12.78 13.80 23.57 10.56 5.10 0.00 12.10 7.95
Chlorite 4.43 7.52 0.00 3.98 3.78 0.00 5.62 3.37 7.98 27.71 4.03 8.63 8.98 9.47 8.34
Muscovite 3.24 0.00 0.00 1.08 1.87 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Enstatite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Goethite_ 0.00 0.00 14.93 4.98 8.62 20.75 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Kaolinite 0.00 0.00 20.95 6.98 12.10 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Ilmenite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Magnetite_ 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Hematite 4.58 0.00 3.89 2.82 2.47 4.94 0.00 0.00 0.00 0.00 2.25 0.00 0.00 0.32 0.85
Hornblende 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Microcline 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 6.20 6.98 1.88 3.22
Orthoclase 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Plagioclase 6.52 18.24 6.37 10.38 6.81 0.00 13.86 3.20 4.41 11.10 6.53 16.81 26.54 11.78 8.20
Quartz 30.50 28.50 36.68 31.89 4.26 74.32 21.45 27.37 14.36 12.74 20.50 12.71 3.77 16.13 7.67
Smectite 39.82 32.95 0.00 24.26 21.29 0.00 40.18 53.28 51.69 0.00 46.51 49.04 44.67 40.77 18.51
Titanite 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Calcite,
magnesian0.00 2.51 0.00 0.84 1.45 0.00 0.00 0.00 7.77 0.00 9.62 0.00 0.00 2.48 4.28
Total 100.00 100.00 100.00 100.00 0.00 100.01 100.00 100.00 100.01 100.00 100.00 100.00 100.00 100.00 0.00
0.00 Zero Values are greyed out to accentuate quantitative values
Average and Standard deviation calculations include samples with zero values
Table C6: XRD results for the Sibasa Basalts at Siloam
Colluvium Residual Basalt
AverageStandard
DeviationAverage
Standard
Deviation
The Influence of Weathering on the Engineering Soil Profile: A study of Low Relief Basalts in South Africa
XRD (wt % )
Highly
Weathered
Basalt
Slightly
Weathered
Basalt
Sample nr S01 S01 S01 SR
Depth (m) 0.0-0.3 0.3-1.0 1.0-2.0 Surface
Augite 0.00 14.52 19.59 24.73
Actinolite 0.00 0.00 0.00 0.00
Diopside 0.00 0.00 0.00 0.00
Epidote 0.00 0.00 0.00 0.00
Chlorite 0.00 0.00 0.00 0.00
Muscovite 0.00 0.00 0.00 0.00
Enstatite 0.00 8.54 0.00 0.00
Goethite_ 0.00 0.00 0.00 0.00
Kaolinite 0.00 0.00 0.00 0.00
Ilmenite 0.00 0.00 0.00 0.00
Magnetite_ 0.00 0.00 0.00 0.00
Hematite 0.00 0.00 0.00 2.24
Hornblende 0.00 0.00 0.00 0.00
Microcline 6.90 11.18 0.00 0.00
Orthoclase 0.00 0.00 0.00 0.00
Plagioclase 6.96 11.23 41.42 43.95
Quartz 34.95 20.39 3.14 5.13
Smectite 51.19 26.37 35.85 23.96
Titanite 0.00 0.00 0.00 0.00
Calcite, magnesian 0.00 7.77 0.00 0.00
Total 100.00 100.00 100.00 100.01
0.00
Residual Basalt
Zero Values are greyed out to accentuate quantitative values
Average and Standard deviation calculations include samples with zero values
Table C7: XRD results for the Springbok Flats Basalt at Codrington